IBA STS MDCAT PAST PAPER 26-10-2025
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چار آپشن میں سے کسی ایک پر کلک کرنے سے جواب سرخ ہو جائے گا۔
- CO₂
- SnCl₂
- CS₂
- HCN
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Explanation
SnCl₂ has two bond pairs and one lone pair, giving it a bent (V-shaped) geometry.
The others (CO₂, CS₂, HCN) have no lone pairs on the central atom, so they are linear.
- CsI
- LiF
- NaCl
- KCl
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Explanation
Lattice energy increases with smaller ionic size and higher charge.
Li⁺ and F⁻ are the smallest ions in the list, so LiF has the highest lattice energy.
- H⁺ reduces
- Cu reduces
- Cu⁺² reduces
- None of these
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Explanation
In the electrochemical cell, the Standard Hydrogen Electrode (SHE) acts as the anode where hydrogen gas is oxidized to H⁺ ions.
The Cu²⁺ ions in the copper electrode are reduced to Cu metal at the cathode.
- TY = 34 g and PY = 33%
- TY = 68 g and PY = 75%
- TY = 34 g and PY = 75%
- None of these
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Explanation
Moles: N₂ = 56/28 = 2 mol, H₂ = 12/2 = 6 mol → stoichiometric (2 mol N₂ needs 6 mol H₂).
Theoretical NH₃ = 2×2 = 4 mol → 4×17 = 68 g; % yield = (51/68)×100 = 75%.
- Zn/Hg conc.HCl
- H₂ and Pd
- LiAlH₄
- None of these
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Explanation
Clemmensen reduction converts aldehydes or ketones to alkanes.
It uses zinc amalgam (Zn/Hg) and concentrated hydrochloric acid as reagents.
- Sp² hybridization
- Fractional bond order
- 6 sites for monosubstitution
- No elimination reaction
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Explanation
Benzene has only 3 distinct sites for monosubstitution due to its symmetry (ortho, meta, para positions).
So, saying 6 sites for monosubstitution is not true about benzene.
- Instantaneous rate is high
- Average rate is high
- Both rates are same
- None of these
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Explanation
At the start, the concentration of reactants is maximum, so collisions occur more frequently.
This makes the instantaneous rate of reaction highest at the beginning.
جب کسی مادے کا ایک تل بخار کے مقابلے میں ترجیحی طور پر گل جاتا ہے تو پھر سڑن _____ ہوتا ہے؟
- Equal energy
- Low energy
- High energy
- None of these
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Explanation
Decomposition occurs more easily than evaporation when it requires less energy to break bonds.
Hence, the substance has low energy of decomposition compared to evaporation.
- Polyester
- Polyvinyl chloride
- Polyvinylpyrrolidone
- None of these
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Explanation
Polyvinyl chloride (PVC) is formed by addition polymerization of vinyl chloride monomers.
Addition polymers are made when unsaturated monomers join without eliminating any molecule.
- 1:4
- 4:1
- 2:3
- None of these
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Explanation
Benzene (C₆H₆) has 12 sigma (σ) bonds and 3 pi (π) bonds.
Ratio = 12:3 = 4:1, showing sigma bonds are four times pi bonds.
