NUMS ENTRY TEST PAST PAPER 2013
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- Hg²⁺
- NH₃
- BF₃
- AlCl₃
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Explanation
Electrophiles are electron-pair acceptors (electron-deficient species).
NH₃ is an electron-pair donor (Lewis base → nucleophile), not an electrophile.
Hg²⁺, BF₃, and AlCl₃ are electron-deficient and act as electrophiles.
- One sigma bond
- One sigma and one Pi bond
- One sigma and two Pi bonds
- None of these
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Explanation
In calcium carbide (CaC₂), the carbide ion is C₂²⁻, where two carbon atoms are linked by a triple bond.
A triple bond consists of 1 sigma bond + 2 pi bonds between the two carbon atoms.
- Lower ionization energy
- Smaller ionic radii
- Greater hardness
- None of these
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Explanation
Alkali metals have larger atomic size than alkaline earth metals, so their outer electrons are farther from the nucleus.
This makes it easier to remove an electron, giving them lower ionization energy than alkaline earth metals.
- Salts formed does not hydrolyze
- Strong base and strong acid react in aqueous solution
- Only H⁺ + OH⁻
- None of these
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Explanation
Strong acids and bases are fully dissociated, so the reaction is always simply H⁺ + OH⁻ → H₂O.No extra energy is absorbed or released from dissociation or hydrolysis of the salt formed, so the heat change is constant.
- 5.6 litres of CO2 at STP is equal to 11 g.
- 8g of O2 at S.T.P occupies a volume of 5.6 liters.
- 1g of H2 in 0.5 liter flask exerts pressure of 24.63 atm at 300K.
- 1 mole of NH3 at 300K and 1 atm occupies volume 22.4 liters.
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Explanation
1 mole of NH₃ at 300 K and 1 atm occupies 22.4 L
Because it deviates from the expected 24.6 L, showing real gas behavior.
- No(28)
- V(23)
- SC(21)
- None of these
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Explanation
Scandium (Z = 21) normally has configuration [Ar] 3d¹ 4s², placing it in the d-block.
If Aufbau principle were not followed, it could instead fill differently (e.g., 4s before 3d), shifting it out of the d-block position.
- Under suitable conditions, graphite can be converted into diamond.
- Both have giant molecular structures
- Complete combustion of equal masses of carbon dioxide as the only product
- None of these
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Explanation
Allotropes are different forms of the same element in the same physical state.
Diamond and graphite are allotropes since both are pure carbon and one can be transformed into the other under suitable conditions.
- When it is generally un-reactive.
- When it contains carbon and hydrogen only.
- When it has the general formula CnH2n+2.
- None of these
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Explanation
Alkanes are saturated hydrocarbons with only single bonds.
Their defining feature is the general formula CₙH₂ₙ₊₂.
- Butane (C4H10)
- Propane (C3H8)
- Ethanol (2H5OH)
- None of these
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Explanation
Ethanol (C₂H₅OH)
C₂H₅OH + 3 O₂ → 2 CO₂ + 3 H₂O
→ 3 moles of H₂O
- 12
- 6
- 8
- None of these
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Explanation
Step 1: Structure of H₂SO₄
Step 2: Count covalent bonds around sulfur
-
Each S=O double bond → 2 covalent bonds × 2 = 4 bonds
-
Each S–O single bond → 1 covalent bond × 2 = 2 bonds
-
Total = 6 covalent bonds around sulfur
Step 3: Electrons in covalent bonds
Each covalent bond = 2 electrons → 6 × 2 = 12 electrons
