Enforcement Officer / Accounts Officer (EO/AO) 2017 recruitment test. Transcribed from the Commission's own booklet (series A, GRS-A-TNS); answer as per the official UPSC final answer key. This question is in Part B. Answer last reviewed 24 August 2026.

Statement I : It is a common observation that if we place a glass of ice-water on a table at room temperature, the ice-water will get warmer. Statement II : Heat is energy that flows between a system and its environment because of temperature difference between them.

(a)Both the statements are individually true and Statement II is the correct explanation of Statement I
(b)Both the statements are individually true but Statement II is not the correct explanation of Statement I
(c)Statement I is true but Statement II is false
(d)Statement I is false but Statement II is true

Answer

Why

Correct — A, (a) Both the statements are individually true and Statement II is the correct explanation of Statement I. This is the second of the two items governed by the Directions block, which the booklet prints once, over the previous question, and does not repeat here. That block tells you to examine the two statements and choose from a four-way code, and the four code entries are the options printed above.

Statement II is the standard physical definition of heat: energy that flows between a system and its environment because of a temperature difference between them. Two things in that sentence are doing work. Heat is energy in transit, not a substance and not something a body stores — a body stores internal energy, and heat is the name for energy while it is crossing the boundary. And the cause of the flow is named: a difference of temperature. The statement is true.

Statement I is an everyday observation and it is also true. A glass of ice-water sits at about 0 degrees Celsius; a room sits at 25 or 30. The environment is the hotter of the two, so energy flows from the room into the glass, and the contents warm until they reach the temperature of the room. Nothing else could happen: energy flows from the hotter body to the colder one, never the other way of its own accord.

And Statement II explains Statement I completely. The observation in Statement I is not merely consistent with the definition in Statement II; it is an instance of it, and the definition supplies both the mechanism and the direction. Because there is a temperature difference, energy flows; because the glass is the colder side, the energy flows into it; because energy flows into it, it gets warmer. So the answer is option (a).

One detail is worth adding for accuracy, since a careful student will notice it. While ice is still floating in the glass, the mixture stays at 0 degrees and its temperature does not rise: the incoming energy is being used as latent heat to melt the ice, roughly 3.3 lakh joules for every kilogram melted. Only when the last of the ice has gone does the temperature of the water begin to climb towards room temperature. Energy is entering the glass throughout; visible warming begins later. This does not disturb the answer — over the period of the observation the ice-water does get warmer — but it is the physics that makes the statement interesting rather than trivial.

As on the companion item, note that the code offers no branch for both statements being false. At least one is true, and Statement II, being a definition drawn from the textbooks, is certainly the true one — which disposes of option (c) at once.

Why the others are wrong

(b)Both the statements are individually true but Statement II is not the correct explanation of Statement I — This branch would be right if the two statements were both true but unconnected, and the temptation to choose it comes from a feeling that a definition cannot ’explain’ an observation. It can, and here it does. Statement II does not merely restate what happens; it identifies the temperature difference as the cause and, by naming heat as a flow between a system and its environment, fixes the direction of that flow. Apply the test that decides every explanation limb: would Statement I still be true if Statement II were false? If energy did not flow because of temperature differences, a cold glass in a warm room would have no reason to warm at all. The dependence is total, so the link is explanatory.
(c)Statement I is true but Statement II is false — This branch condemns Statement II, which is the definition of heat given in every standard physics text. Nothing in it is open to doubt. A candidate sometimes lands here after quarrelling with the word ’flows’, on the ground that heat is not a fluid — the caloric theory having been abandoned in the nineteenth century. But ’flows’ here describes a transfer of energy across a boundary, which is exactly what the modern account says happens; it is a description of transit, not a claim about substance. The wording is the textbook’s own.
(d)Statement I is false but Statement II is true — This branch condemns Statement I, and the objection behind it is usually the latent heat point: while ice remains, the temperature of the mixture stays at 0 degrees, so for a while nothing gets warmer in the sense of a rising thermometer. That is good physics but it is not a refutation. Statement I describes what happens when a glass of ice-water is left standing in a warm room, and what happens is that the ice melts and the water then warms to room temperature; the mixture ends warmer than it began. A statement in an item of this kind is to be read as it would be read by a competent reader, not stretched to the instant after it is set down. The general lesson is worth carrying: on this format, do not manufacture a falsehood out of a qualification the statement did not need to make.

Concept

Temperature and heat are different quantities and the item turns on the difference. Temperature is a property a body has, and the zeroth law of thermodynamics is what makes it meaningful: if two bodies are each in thermal equilibrium with a third, they are in thermal equilibrium with each other, and the property they share can be measured on a common scale. Heat is not a property at all. It is energy in transit across the boundary of a system, driven by a temperature difference, and once the transfer has happened the energy is simply part of the internal energy of the receiving body — it is not stored there as heat. The direction is fixed: energy flows spontaneously from the body at higher temperature to the body at lower temperature, and the second law of thermodynamics is the statement that it never does the reverse unaided. Transfer stops when the temperatures are equal, which is thermal equilibrium. Two further ideas complete the picture for the glass of ice-water. Specific heat capacity is the energy needed to raise the temperature of unit mass by one degree, and it governs the warming of the water once the ice has gone. Latent heat is the energy absorbed at a change of state with no change of temperature at all — about 3.3 lakh joules per kilogram for the melting of ice — and it governs the earlier phase, when energy pours in and the thermometer does not move. Both are the same heat, doing different work.

General science in an EPFO paper is set at the level of a good school textbook, and thermodynamics is reliably represented because its basic distinctions can be tested in a single sentence. The definitions to hold cleanly are heat against temperature, heat against internal energy, and specific heat against latent heat. Set inside the Statement I and Statement II format, the topic asks something extra: not just whether you know the definition of heat, but whether you can see that a definition can serve as the explanation of an observation. It can, whenever the definition names the cause. That is the discriminating question on the explanation limb, and it is worth rehearsing on easy examples before meeting it in an examination.

Key facts

Heat is energy transferred between a system and its environment because of a temperature difference between them.
Heat is energy in transit; a body possesses internal energy, not heat.
Energy flows spontaneously from the body at the higher temperature to the body at the lower temperature, and never the reverse without external work.
Transfer ceases when the two temperatures are equal — the state of thermal equilibrium.
The zeroth law of thermodynamics — two bodies each in thermal equilibrium with a third are in equilibrium with each other — is what makes temperature a measurable property.
While ice is melting, absorbed energy goes into latent heat and the temperature of the ice-water mixture stays at 0 degrees Celsius.
The latent heat of fusion of ice is about 3.3 lakh joules per kilogram.
Specific heat capacity governs the temperature rise of the water after all the ice has melted.
The Directions block governing this item is printed above the previous question and is not reprinted here; its code has no branch for both statements being false.

Heat is energy in transit, and the definition supplies both the mechanism and the direction

Statement II is true→The standard physical definition: heat is energy that flows between a system and its environment because of a temperature difference between them. Heat is energy in transit, not a substance and not something a body stores — a body stores internal energy, and heat is the name for energy while it is crossing the boundary.

Statement I is true→A glass of ice-water sits at about 0 degrees Celsius and a room at 25 or 30, so the environment is the hotter of the two and energy flows into the glass. Nothing else could happen: energy flows from the hotter body to the colder one, never the other way of its own accord.

And II explains I completely→Because there is a temperature difference, energy flows; because the glass is the colder side, it flows into it; because energy flows into it, it gets warmer. The definition does not merely sit consistently beside the observation — it identifies the cause and fixes the direction.

The subtlety that tempts branch (d)→While ice is still floating in the glass, the mixture stays at 0 degrees and the thermometer does not move: the incoming energy is going into latent heat, about 3.3 lakh joules for every kilogram melted. Only when the last of the ice has gone does the water begin to climb towards room temperature. Energy enters throughout; visible warming begins later.

Why that does not falsify Statement I→It describes what happens when a glass of ice-water is left standing in a warm room — the ice melts and the water then warms, and the mixture ends warmer than it began. A statement in this format is to be read as a competent reader would read it, not stretched to the instant after it is set down.

The quarrel behind branch (c)→That heat is not a fluid, the caloric theory having been abandoned in the nineteenth century, so it cannot ‘flow’. But the word here describes a transfer of energy across a boundary, which is exactly what the modern account says happens — a description of transit, not a claim about substance, and the wording is the textbook’s own.

Study next

The zeroth and first laws of thermodynamics, and the distinction between heat, work and internal energySpecific heat capacity and latent heat, with the standard values for water and iceConduction, convection and radiation as the three modes of heat transferThe second law of thermodynamics and why heat flows only one way unaidedThermal expansion, and the anomalous expansion of water between 0 and 4 degrees Celsius

Common traps

Treating heat as something a body contains. A body contains internal energy; heat is the transfer.
Assuming that absorbing heat must raise a temperature. During melting or boiling it does not.
Choosing branch (b) because a definition seems too general to explain a particular observation. A definition that names the cause does explain it.
Manufacturing a false statement out of a qualification the statement did not have to make; the latent heat phase does not make Statement I false.
Forgetting that this code has no both-false branch, and so missing a free elimination.

Thermodynamics reaches these papers as definitional items, as everyday-observation items, and occasionally as a Statement I and Statement II pair like this one. The preparation is the same: hold each definition in a single sentence that names the cause, because it is the cause-naming clause that lets a definition serve as an explanation. When the pair format is used in science, expect the second statement to be a law or a definition, expect it to be true, and spend your time on the first statement and on the link.

Related PYQs

EPFO_EOAO_2017_Q91Open & attempt →

Directions : The following two (2) items consist of two statements, Statement I and Statement II. Examine these two statements carefully and select the correct answer using the code given below. Code : (a) Both the statements are individually true and Statement II is the correct explanation of Statement I (b) Both the statements are individually true but Statement II is not the correct explanation of Statement I (c) Statement I is true but Statement II is false (d) Statement I is false but Statement II is true Statement I : The force on Moon due to Earth is the action, while the force on Earth due to Moon is the reaction. Statement II : To every action, there is an equal and opposite reaction.

(a) Both the statements are individually true and Statement II is the correct explanation of Statement I
(b) Both the statements are individually true but Statement II is not the correct explanation of Statement I
(c) Statement I is true but Statement II is false
(d) Statement I is false but Statement II is true

Answer(a) Both the statements are individually true and Statement II is the correct explanation of Statement I

The first of the two items governed by the shared Directions block, on Newton’s third law and the Earth-Moon force pair; the block and its four-way code are printed over that question and cover this one too.

Practice

practice — not a real PYQ
Energy supplied to a mixture of ice and water at 0 degrees Celsius, while ice is still present, produces
- (a)a steady rise in the temperature of the mixture
- (b)melting of the ice with no change in temperature
- (c)a fall in the temperature of the mixture
- (d)no change at all in the mixture
Answer(b) melting of the ice with no change in temperature
practice — not a real PYQ
Which law of thermodynamics justifies the use of a thermometer, by asserting that two bodies each in thermal equilibrium with a third are in thermal equilibrium with each other?
- (a)The zeroth law
- (b)The first law
- (c)The second law
- (d)The third law
Answer(a) The zeroth law