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NEET Mole Concept: 5 practice MCQs with answers

By the PrepMatic team · Updated 9 Oct 2026 · 4 min read

The mole concept is the arithmetic of chemistry, and almost every numerical in Physical Chemistry rests on it. The five MCQs below cover the number of molecules in a given mass, a limiting reagent problem, molarity, an empirical formula and a concentration unit that does not change with temperature. They are at NCERT Class 11 level.

What this chapter covers in the NEET syllabus

The NMC unit is Some Basic Concepts of Chemistry, which is the first chapter of Class 11 Chemistry in NCERT. The topics are:

• Matter, its classification, and the laws of chemical combination.
• Atomic and molecular masses, the mole, Avogadro's number and molar mass.
• Percentage composition, empirical formula and molecular formula.
• Chemical equations and stoichiometry, including the limiting reagent.
• Concentration of solutions: mass percent, mole fraction, molarity and molality.
• Significant figures and units in calculations.

Five practice MCQs on the Mole Concept

Question 1

The number of molecules in 4.4 g of CO₂ is (molar mass of CO₂ = 44 g/mol; NA = 6.022 × 10²³ mol⁻¹):

• A. 6.022 × 10²²
• B. 6.022 × 10²³
• C. 1.2044 × 10²³
• D. 6.022 × 10²¹

Question 2

In the reaction 2H₂ + O₂ → 2H₂O, 4 g of H₂ reacts with 16 g of O₂. The mass of water formed is:

• A. 20 g
• B. 36 g
• C. 18 g
• D. 9 g

Question 3

The molarity of a solution made by dissolving 4 g of NaOH (molar mass 40 g/mol) in enough water to make 500 mL of solution is:

• A. 0.1 M
• B. 0.2 M
• C. 0.4 M
• D. 2 M

Question 4

A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass. Its empirical formula is (C = 12, H = 1, O = 16):

• A. CHO
• B. C₂H₄O
• C. CH₂O
• D. CH₃O

Question 5

Which of the following concentration terms does not change with temperature?

• A. Molarity
• B. Normality
• C. Percentage weight by volume
• D. Molality

Answers and explanations

1. A. Moles = 4.4/44 = 0.1 mol. Number of molecules = 0.1 × 6.022 × 10²³ = 6.022 × 10²². Option B is the number in a full mole (44 g).
2. C. 4 g of H₂ is 2 mol, and 16 g of O₂ is 0.5 mol. The equation needs 1 mol of O₂ for 2 mol of H₂, so O₂ is the limiting reagent. 0.5 mol of O₂ forms 1 mol of H₂O, which is 18 g. The sum of the two masses (20 g) is not the answer, because H₂ is in excess.
3. B. Moles of NaOH = 4/40 = 0.1 mol. Volume = 0.5 L, so molarity = 0.1/0.5 = 0.2 M. The most common slip is to forget to convert mL to L.
4. C. Taking 100 g of the compound: C = 40/12 = 3.33, H = 6.7/1 = 6.7, O = 53.3/16 = 3.33 mol. Dividing by 3.33 gives C : H : O = 1 : 2 : 1, so the empirical formula is CH₂O.
5. D. Molality is moles of solute per kilogram of solvent, and mass does not change with temperature. Molarity, normality and % w/v all depend on the volume of the solution, which expands on heating. Mole fraction is also temperature-independent, though it is not among the options.

How to prepare the Mole Concept

• Convert everything to moles first. Whatever the question gives (mass, volume of gas at STP, number of particles, solution volume and molarity), the first step is to find moles. Then use the balanced equation or the formula.
• Keep a conversion map. Moles = mass/molar mass = number of particles/NA = volume at STP/22.4 L for gases (at 273 K and 1 bar the molar volume is 22.7 L, so read the question to see which value is assumed). Moles = molarity × volume in litres.
• Solve limiting reagent problems by comparing mole ratios. Divide the moles of each reactant by its coefficient. The smaller value is the limiting reagent, and products depend on that one.
• Know the concentration terms and their units. Molarity is mol/L of solution, molality is mol/kg of solvent, and the mole fraction has no unit. Practise converting between them using density.
• Check percentage composition questions by summing to 100. Empirical formula steps are always: mass or percent, moles, simplest ratio, whole numbers.

This chapter is small but is used everywhere else, so build speed with a daily set of ten problems for a week. For where Chemistry fits in your plan, see the NEET Chemistry preparation guide, and for NCERT reading tips, NCERT for NEET.

Take a full Mole Concept test on PrepMatic

Mole Concept errors are usually arithmetic slips, and a timed test brings them out. PrepMatic's topic tests run about 15 questions in 30 minutes with NEET's negative marking. The free Basic plan includes topic tests, and the practice hub lists the next chapter.

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