SPSC CHEMISTRY 25 YEARS PAST PAPERS
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چار آپشن میں سے کسی ایک پر کلک کرنے سے جواب سرخ ہو جائے گا۔
- 10
- 8
- 4
- None of these
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Explanation
For a strong acid with a high Ka value (10.8), it fully ionizes in water.pH is calculated as , and for a 1 M strong acid, , so pH = 4.
کیلشیم اور فاسفیٹ پر مشتمل پانی کو _____ کہا جاتا ہے؟
- Permanent hard water
- Permanent soft water
- Temporary hard water
- None of these
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Explanation
Temporary hard water contains dissolved calcium and magnesium bicarbonates, which can be removed by boiling.It differs from permanent hard water, which contains sulfates or chlorides that do not precipitate upon heating.
- CH3I
- CH3Br
- CH3Cl
- None of these
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Explanation
SN2 reactions favor weaker C-X bonds, and iodine (I) has the weakest bond due to its large atomic size.CH₃I reacts fastest because iodide is a better leaving group than Br, Cl, or F.
- Basic in nature
- Acidic in nature
- Natural compounds
- None of these
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Explanation
Phenols are weak acids due to the ability to donate a proton (H⁺).The phenoxide ion is stabilized by resonance, making phenols more acidic than alcohols.
- CN⁻
- NO
- O2
- None of these
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Explanation
Two species are isoelectronic if they have the same number of electrons.
N₂ has 14 electrons (7 from each nitrogen atom).
CN⁻ also has 14 electrons (6 from carbon, 7 from nitrogen, and 1 extra due to the negative charge).
کسی عنصر کی شناخت ______ کے ذریعہ طے کی جاتی ہے؟
- The number of its electron
- The number of its neutron
- The number of its proton
- None of these
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Explanation
The atomic number (number of protons) uniquely identifies an element.Changing the number of protons changes the element itself, while electrons and neutrons can vary.
- 1s^2 2s^2 2p^4
- 1s^2 2s^2 2p^6
- 1s^2 2s^2 2p^6 3s^2 3p^2
- None of these
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Explanation
Magnesium (Mg) has 12 electrons with a neutral configuration of 1s² 2s² 2p⁶ 3s².Mg²⁺ loses 2 electrons from the outermost 3s² orbital, leaving 1s² 2s² 2p⁶.
- 38 miles
- 19 moles
- 13 moles
- None of these
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Explanation
Balanced Equation:
The coefficient of O₂ is 19, meaning 19 moles of O₂ are required.
مندرجہ ذیل میں سے کون سا ٹرانزیشن سب سے زیادہ توانائی کی منتقلی ہے؟
- n to σ∗
- n to π∗
- σ to σ∗
- None of these
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Explanation
σ to σ* transition requires the highest energy.
Because it involves the breaking of a strong sigma bond.
فینول سائکلوہیکسنول سے بہتر برونسٹڈ ایسڈ ہے جس کی بڑی وجہ _____ ہے؟
- It is a better proton donor
- The phenyl group is an electron withdrawing group by induction, which stabilizes the action formed in the reaction
- Phenol is able to stabilize the anion formed in the reaction by resonance
- None of these
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Explanation
Phenol's conjugate base (phenoxide ion) is stabilized by resonance, spreading the negative charge over the benzene ring.Cyclohexanol lacks resonance stabilization, making its conjugate base less stable and less acidic.
