NUMS ENTRY TEST PAST PAPER 2013
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- Solubility in water
- Boiling point
- Molecular mass
- None of these
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Explanation
The rate of diffusion/effusion of a gas is inversely proportional to the square root of its molecular mass (Graham’s law).
Lighter gases spread faster in the laboratory than heavier gases.
- 3.6 × 10²⁴
- 3.6 × 10²³
- 6.0 × 10²³
- None of these
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Explanation
Step 1: Molar mass of glucose
C₆H₁₂O₆ = (6×12) + (12×1) + (6×16) = 72 + 12 + 96 = 180 g/mol.
Step 2: Moles in 18 g
n=18018=0.1 molStep 3: Molecules in 0.1 mol
1 mol = 6.022 × 10²³ molecules
0.1 mol = 6.022 × 10²² molecules.
Step 4: Carbon atoms per molecule
Each glucose molecule has 6 carbon atoms.
Total carbon atoms = 6 × (6.022 × 10²²) = 3.6132 × 10²³.
- Xenon
- Chlorine
- Neon
- None of these
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Explanation
Chlorine free radicals (Cl·) from CFCs react with ozone (O₃), breaking it into O₂ and ClO·.
This chain reaction depletes the ozone layer and one Cl· can destroy thousands of ozone molecules.
- Cyclohexane
- Benzene
- Methane
- None of the above
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Explanation
In CH₄ (methane), the carbon is sp³ hybridized.
It giving a tetrahedral geometry with bond angles of 109.5°.
- Aqueous sodium hydroxide and benzoyl chloride
- Aqueous bromine
- Aqueous sodium hydroxide
- None of these
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Explanation
Phenol is weakly acidic and dissolves in aqueous NaOH to form sodium phenoxide → giving a clear, colorless homogeneous solution.
It does not dissolve completely in water or Na₂CO₃ because it is not acidic enough to react fully with weaker bases.
- The freezing of the water
- The condensation
- The electrolysis of water
- None of these
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Explanation
Electrolysis of water requires an external supply of electrical energy to break bonds → endothermic.
Condensation and freezing release heat (exothermic processes).
- A catalyst will lower the activation energy of reaction.
- A catalyst will speed up the rate determining step.
- Catalyst will be used up in a reaction.
- A catalyst may induce steric strain in a molecule to make it react more readily.
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Explanation
A catalyst is not consumed during a chemical reaction; it remains unchanged at the end.
It works by lowering activation energy and providing an alternate pathway for the reaction.
- Ionic crystals
- Molecular crystals
- Metallic crystals
- None of these
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Explanation
Molecular crystals are held together by weak van der Waals forces or hydrogen bonds.
Examples include crystals of ice, iodine, naphthalene, etc.
- Increases
- Change
- Stay roughly the same
- None of these
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Explanation
Elements in the same group have the same number of valence electrons, so their chemical properties remain similar.
However, their reactivity trends (increase or decrease) may vary down the group, but overall chemical nature stays roughly the same.
- It has the same mass as 1 mole of carbon atoms.
- It is liberated by 1 mole electrons.
- It contains the same number of atoms as 1 mole of hydrogen atoms.
- It contains the same number of atoms as 1/2 mole of C¹².
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Explanation
By definition, 1 mole of any element contains Avogadro’s number (6.022 × 10²³) of atoms.
So, 1 mole of a metal has the same number of atoms as 1 mole of hydrogen atoms.
