NEET (UG)

Practice Test 1 — Some Basic Concepts of Chemistry

12 questions • 18 minutes • auto-graded with full solutions

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Section A — MCQ (Single Correct)

Question 1

The law of definite proportions states that a compound has a fixed:

Solution: Elements combine in a fixed mass ratio.

Question 2

One mole of any substance contains:

Solution: Avogadro's number $= 6.022\times10^{23}$.

Question 3

The number of moles in $44\ \text{g}$ of $\text{CO}_2$ (molar mass $44$) is:

Solution: $n = 44/44 = 1\ \text{mol}$.

Question 4

The volume of $1\ \text{mol}$ of an ideal gas at STP is:

Solution: $22.4\ \text{L/mol}$ at STP.

Question 5

The empirical formula of a compound with $\text{C}:\text{H} = 1:2$ mole ratio is:

Solution: Simplest ratio $1:2$ gives $\text{CH}_2$.

Question 6

The reactant consumed completely first is the:

Solution: Limiting reagent decides the product amount.

Question 7

Molality is moles of solute per:

Solution: $m = $ moles / kg of solvent.

Question 8

The molarity of $1\ \text{mol}$ solute in $2\ \text{L}$ of solution is:

Solution: $M = 1/2 = 0.5\ \text{M}$.

Section B — Assertion & Reason

Question 9

A: The molality of a solution does not change with temperature.
R: Molality is defined in terms of the mass of solvent, which is independent of temperature.

Solution: Mass does not vary with temperature, so molality is constant — R explains A.

Question 10

A: $\text{CO}$ and $\text{CO}_2$ obey the law of multiple proportions.
R: The masses of oxygen combining with a fixed mass of carbon are in a simple whole-number ratio.

Solution: The $1:2$ oxygen ratio is exactly the law of multiple proportions — R explains A.

Question 11

A: The molarity of a solution increases when its temperature is raised.
R: The volume of a solution increases with temperature.

Solution: As volume increases with temperature, molarity (moles/volume) decreases, so A is false; R correctly states volume rises.

Question 12

A: The empirical and molecular formulae of a compound can be identical.
R: The molecular formula is always a whole-number multiple of the empirical formula.

Solution: When the multiple is 1 (e.g. water), the two are identical — R explains A.