SSC CGL 2024 Tier-I · 26 September 2024, Shift 1 · General Awareness · Question 22 of 100

Text as printed on a candidate's response sheet for this shift; answer per SSC's tentative key as marked on that sheet. Solution last reviewed 10 September 2026.

Where this paper and its answers come from

SSC does not publish CGL question papers or a public answer key. The questions and options here are reproduced as printed on a candidate's own response sheet for this shift — the Commission's text, unchanged. Each answer is SSC's tentative key as marked on that sheet; SSC allowed challenges to it and never publishes a final key. The solutions are written by UnlockIAS.

Which of the following statements is NOT correct?

(a)Light year is the unit of distance.
(b)Light year is the distance travelled by light in one year.
(c)Light year is the unit of time.
(d)Angstrom is unit of length.

Answer

Why

Correct — C. The stem asks which statement is NOT correct, so the answer is the false one.

A light year measures distance, not time. It is how far light travels in a vacuum in one year — about 9.46 × 10¹² km.

The word year names the interval used to define that distance, which is what makes option (c) sound plausible and still leaves it false.

The statements at (a), (b) and (d) are each true, so the exception the stem wants is option (c).

Why the others are wrong

(a)
Light year is the unit of distance. — Light year is a unit of distance — a true statement, so it cannot be the one that is NOT correct. Astronomers use it because stellar distances are unwieldy in kilometres.
(b)
Light year is the distance travelled by light in one year. — The distance travelled by light in one year is the definition of a light year. True as well, so this is not the exception the stem is hunting for.
(d)
Angstrom is unit of length. — Angstrom is a unit of length, equal to 10⁻¹⁰ metre or 0.1 nanometre, used for atomic sizes and wavelengths. True again, so not the odd one out.

Concept

Two units on this list measure the same quantity — length — at opposite ends of the scale.

The light year is about 9.46 × 10¹² km, the distance light covers in a year at roughly 3 × 10⁸ m/s. The angstrom is 10⁻¹⁰ m, small enough to state the size of an atom.

Neither is an SI unit. The SI unit of length is the metre, and both of these are convenience units defined in terms of it — one for the sky, one for the atom.

A NOT-correct stem reverses the usual reading, and that is where the marks go.

Mark each statement true or false first, then pick the false one. Candidates lose this question by finding a statement that is plainly true and stopping there.

Key facts

A light year is a unit of distance, about 9.46 × 10¹² km.
One angstrom is 10⁻¹⁰ metre, or 0.1 nanometre.
The SI unit of length is the metre.
Light travels at about 3 × 10⁸ metres per second in a vacuum.

Study next

Astronomical distance units — light year, astronomical unit and parsecSI base units and the quantity each one measuresNon-SI units still in everyday scientific use, such as the angstrom and the electron volt

Common traps

Answering (a) because it is the first true statement you read, when the stem wants the false one.
Hearing the word year inside light year and filing the unit under time.

SSC runs unit questions in both directions.

The NOT form was keyed on 19 Sep 2024, 09:00, GA Q.15 — Joule, kilowatt hour, calorie and Newton, with Newton the one that is not a unit of energy.

The straight form appears on 11 Sep 2024, 12:30, GA Q.13 (diopter for the power of a lens) and 26 Sep 2024, 16:00, GA Q.3 (ohm metre for specific resistance).

Related PYQs

No directly related past PYQ was found.