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NEET Chemistry MCQ
Quiz 3
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Q.1
Which of the following statements about a compound is incorrect?
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A molecule of a compound has atoms of different elements.
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The ratio of atoms of different elements in a compound is fixed.
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A compound retains the physical properties of its constituent elements.
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A compound cannot be separated into its constituent elements by physical methods of separation.
Explanation
A compound's properties are typically completely different from those of its constituent elements — e.g. water (a liquid) bears no resemblance to hydrogen and oxygen gases. So the claim that a compound "retains the physical properties of its constituent elements" is the incorrect statement; compounds are chemically combined in fixed ratios and can't be separated by physical means, which the other statements correctly describe.
Q.2
Weight of one atom of an element is $6.644 \times 10^{-23} \ g $. Calculate g-atom of elements in 40 kg
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$10^4 \ g-atom$
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$10^3 \ g-atom$
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$10^5 \ g-atom$
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$10^2 \ g-atom$
Explanation
Number of atoms in 40 kg (40,000 g) = 40000 / (6.644×10⁻²³) ≈ 6.02×10²⁶ atoms. Gram-atoms (moles) = 6.02×10²⁶ / 6.022×10²³ ≈ 1000 = 10³ g-atom.
Q.3
How many gram of concentrated hydrochloric acid containing 37.9% HCl by weight will contain 6 g of HCl?
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15.84 g
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14.1 g
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13.6 g
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11.2 g
Explanation
If x grams of solution contain 37.9% HCl by weight, and that equals 6 g of HCl: 0.379 × x = 6 → x = 6/0.379 ≈ 15.84 g.
Q.4
The volume of 1.0 g of hydrogen in litres at N.T.P is
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11.2
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2.24
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22.4
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1.12
Explanation
Hydrogen (H₂) has molar mass 2 g/mol. Moles in 1.0 g = 1.0/2 = 0.5 mol. Volume at NTP = 0.5 × 22.4 L = 11.2 L.
Q.5
The unit of Molar mass is
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gm/moles
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None of the these
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moles/gm
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g moles
Explanation
Molar mass is defined as mass per mole of a substance, so its unit is grams per mole (g/mol).
Q.6
The sum of the mole fraction of all the components in a solution is
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0
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None of the above
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-1
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1
Explanation
By definition, mole fractions represent the proportion each component contributes to the total moles present, so they must always add up to exactly 1.
Q.7
If 500 mL of a 5M solution is diluted to 2500 mL, what will be the molarity of the solution obtained
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1.59 M
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0.017 M
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1.0 M
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1.66 M
Explanation
Using M₁V₁ = M₂V₂ (moles stay constant on dilution): 5 M × 500 mL = M₂ × 2500 mL → M₂ = 2500/2500 = 1.0 M.
Q.8
If 20.0 mL of 1 M CaCl2 and 60 mL of .200 M CaCl2 are mixed, the molarity of the final solution will be
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.8 M
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.1 M
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.5 M
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.4 M
Explanation
Moles from each solution: 0.020 L × 1 M = 0.02 mol, and 0.060 L × 0.200 M = 0.012 mol. Total moles = 0.032 mol. Total volume = 20 + 60 = 80 mL = 0.08 L. Molarity = 0.032/0.08 = 0.4 M.
Q.9
Which of the following statements indicates that law of multiple proportion is being followed
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When magnesium burns in oxygen, the amount of magnesium taken for the reaction is equal to the amount of magnesium in magnesium oxide formed
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Sample of carbon dioxide taken from any source will always have carbon and oxygen in the ratio 1:2.
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Carbon forms two oxides namely CO2 and CO, where masses of oxygen which combine with fixed mass of carbon are in the simple ratio 2:1.
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At constant temperature and pressure 200 mL of hydrogen will combine with 100 mL oxygen to produce 200 mL of water vapour.
Explanation
The law of multiple proportions applies when two elements form more than one compound: the masses of one element that combine with a fixed mass of the other must be in a simple whole-number ratio. Carbon forming CO₂ (2 oxygens per carbon) and CO (1 oxygen per carbon) — a 2:1 ratio of oxygen for the same amount of carbon — is a textbook example of exactly this law.
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