Which one among the following statements about matter is NOT correct?

Correct — B, the claim that the maximum temperature at which a solid melts to become a liquid at atmospheric pressure is called its melting point. The standard definition runs the other way: the melting point is the minimum temperature at which a solid turns into a liquid at atmospheric pressure. The word 'maximum' is what breaks the statement. Below the melting point the solid stays solid however long you wait; at that temperature it begins to melt, and any temperature above it will also melt the solid, so there is no maximum. The other three statements are all sound, which leaves this one as the answer to a 'NOT correct' stem.

• (a)On increasing the temperature of solids, the kinetic energy of particles increases — Raising the temperature of a solid does increase the kinetic energy of its particles — that is what temperature measures. The particles vibrate more strongly about their lattice positions until the vibration overcomes the forces holding the lattice together.
• (c)Particles of steam have more energy than water at 100°C — Steam at 100 degrees Celsius does hold more energy than water at the same temperature. The extra amount is the latent heat of vaporisation, about 2,260 kilojoules for every kilogram, absorbed without any rise in temperature. It is why a steam burn is worse than a boiling-water burn.
• (d)Direct change of gas to solid is called deposition — The direct change from gas to solid is indeed called deposition, and the reverse change from solid to gas is sublimation. Frost forming on a cold surface is the everyday example.

A pure substance changes state at fixed temperatures under a fixed pressure. Heat supplied during a change of state does not raise the temperature at all; it goes into breaking the forces between particles and is called latent heat. The latent heat of fusion of ice is about 334 kilojoules per kilogram, while the latent heat of vaporisation of water is about 2,260 kilojoules per kilogram, which is why boiling a pan dry takes so much longer than melting the same mass of ice.

Three of the four statements read straight out of the school chapter on matter, and the fourth has been altered by a single word. That is the format to watch for in a 'which is NOT correct' item: scan for the quantifier rather than the content. 'Maximum' where the textbook says 'minimum', 'always' where it says 'usually', 'directly' where it says 'inversely' — one word carries the whole error. Here the definition is worth carrying verbatim: the melting point is the minimum temperature at which a solid melts at atmospheric pressure.

• Melting point is the minimum temperature at which a solid becomes liquid at atmospheric pressure.
• Latent heat is absorbed or released at constant temperature during a change of state.
• Latent heat of fusion of ice is about 334 kJ/kg; latent heat of vaporisation of water is about 2,260 kJ/kg.
• Steam at 100 degrees Celsius carries more energy than water at 100 degrees Celsius, by the latent heat of vaporisation.
• Gas to solid directly is deposition; solid to gas directly is sublimation.

• Skimming past 'maximum' because the rest of the sentence looks familiar.
• Believing steam and boiling water at 100 degrees hold the same energy.
• Swapping the names sublimation and deposition.

A 'which is NOT correct' item where three statements are textbook-exact and the fourth has one quantifier altered.

• practice — not a real PYQ

  The heat absorbed at constant temperature when a solid turns into a liquid is called its

  • (a)specific heat capacity
  • (b)latent heat of fusion
  • (c)latent heat of vaporisation
  • (d)thermal conductivity

  Answer(b) latent heat of fusion — about 334 kJ per kilogram for ice.

• practice — not a real PYQ

  Camphor left in the open disappears without wetting the surface beneath. The change involved is

  • (a)condensation
  • (b)deposition
  • (c)sublimation
  • (d)fusion

  Answer(c) sublimation — the solid passes straight into the vapour state.