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۔
کم سے کم مستحکم کاربنین _____ ہے؟
- (CH₃)₃C⁻
- CH₃⁻
- (CH₃)₂C⁻
- None of these
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Explanation
The tertiary carbanion (CH₃)₃C⁻ is the least stable because the negative charge is not effectively stabilized by resonance or inductive effects.Tertiary carbanions are highly unstable compared to secondary and primary carbanions.
فارمک ایسڈ اور ایسٹک ایسڈ ______ کے ساتھ رد عمل کے ذریعہ ایک دوسرے سے ممتاز ہیں؟
- FeCl3
- N3OH
- HgCl2
- None of these
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Explanation
Formic acid (HCOOH) reacts with HgCl₂ to form mercuric formate, while acetic acid (CH₃COOH) does not. This distinguishes the two acids.The presence of the aldehyde group in formic acid makes it reactive with HgCl₂, whereas acetic acid lacks such reactivity.
- Free energy of formation be zero
- Free energy of formation be positive
- Free energy of formation be negative
- None of these
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Explanation
For a 2n interface (e.g., grain boundary, phase boundary) to be stable, the free energy of formation (γ) must be negative.
This ensures that the interface is energetically favorable and can exist stably.
اگر فوٹوون کی لہر کی لمبائی دوگنی ______ ہے؟
- Energy is doubled
- Frequency is doubled
- Energy is reduced by the factor of two
- None of these
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Explanation
Energy of a photon is given by , so if the wavelength () is doubled, energy () is halved.Frequency () and wavelength () are inversely related (), so doubling reduces by half.
مکمل سیل آریگرام میں دو آدھے خلیوں کو ڈبل عمودی لائن سے الگ کیا جاتا ہے جو نمائندگی کرتا ہے؟
- Inert electrode
- Salt bridge
- Cathode half cell
- None of these
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Explanation
In a complete cell diagram, a double vertical line (||) represents the salt bridge.
It allows ion flow to maintain electrical neutrality.
- H2 gas
- Alcoholic KOH
- KMnO4
- None of these
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Explanation
Ethyne (C₂H₂) can be prepared from 1,2-dibromoethane by dehydrohalogenation using alcoholic KOH.Alcoholic KOH promotes elimination (E2 reaction), removing HBr to form ethyne.
کروموتھراپی میں موبائل مرحلے کو _____ کہا جاتا ہے؟
- Fluent
- Elution
- Eluate
- None of these
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Explanation
In chromatography, the mobile phase that carries the sample through the stationary phase is called the eluent.The eluate is the substance that comes out of the column after separation.
- Positron is changed into electrons
- Neutron is changed into proton
- Proton is changed into neutron
- None of these
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Explanation
In β⁻ decay, a neutron inside the nucleus converts into a proton, emitting a beta particle (electron) and an antineutrino.This process increases the atomic number by +1 while keeping the mass number unchanged.
- 800 ml per second
- 400 ml per second
- 160 ml per second
- None of these
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Explanation
The rate of effusion follows Graham’s law: Rate ∝ 1/√Molar mass.Since H₂ (2 g/mol) is lighter than O₂ (32 g/mol), it escapes √(32/2) = 4 times faster, meaning 100 × 4 = 400 ml/sec.
مندرجہ ذیل میں سے کون سا عمل اتپریرک استعمال نہیں کرتا ہے؟
- Contact process
- Haber process
- Thermite process
- None of these
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Explanation
Thermite is a redox reaction that happens on its own.
It doesn't need a catalyst.
Haber's process, Contact process, and Ostwald's process need a catalyst.
