SPSC 25 years Past Papers 2001 to 2025

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SPSC 25 years Past Papers 2001 to 2025

Q1671: The least stable carbanion is _____?

کم سے کم مستحکم کاربنین _____ ہے؟

(CH₃)₃C⁻

CH₃⁻

(CH₃)₂C⁻

None of these

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.

Q1672: How much energy is required to boil a kettle of water containing 1 litre at 15°C (Specific heat capacity of water = 4.18?

3.5 kJ

3550 kJ

355 kJ

None of these

Explanation

To boil 1 liter of water from 15°C to 100°C, the energy required is:

Q = mcΔT

= 1 kg × 4.18 kJ/kg°C × (100°C - 15°C)

= 1 × 4.18 × 85

= 355 kJ

Q1673: The correct order of spectral regions with respect to increasing frequency is _____?

بڑھتی ہوئی تعدد کے سلسلے میں ورنکرم علاقوں کا صحیح حکم _____ ہے؟

UV, ViS, IR, RF

UV,ViS, RF, IR

RF, IR, ViS, UV

None of these

Explanation

RF (Radio frequency) has the lowest frequency, followed by IR (Infrared), ViS (Visible spectrum), and then UV (Ultraviolet), which has the highest frequency.

This order follows the sequence of increasing frequency in the electromagnetic spectrum.

Q1674: Which one among the pairs cannot be separated by H2S in dilute HCl?

Cu^2+, Zn^2+

Bi^3+, Sn^4+

Al^3+, Hg^2+

None of these

Explanation

H₂S in dilute HCl is used to separate metal ions based on their solubility as sulfides.

Bi³⁺ and Sn⁴⁺ do not separate easily.

Because they both form insoluble sulfides under similar conditions.

Q1675: What is pH of a 1 molar solution of an acid that has a Ka - 10.8?

None of these

Explanation

For a strong acid with a high $K_a$ value (10.8), it fully ionizes in water.

pH is calculated as $pH = -log[H^+]$ , and for a 1 M strong acid, $[H^+] = 10^{-4}$ , so pH = 4.

Q1676: The velocity of em waves is ______?

برقی مقناطیسی لہروں کی رفتار ______ ہے؟

1 × 10⁶ m/s

1 × 10⁸ m/s

3 × 10⁸ m/s

None of these

Explanation

The velocity of electromagnetic waves (EM waves) in a vacuum is approximately 3 × 10⁸ meters per second.

This speed is constant for all EM waves, including light, radio waves, and X-rays, in a vacuum.

Q1677: Select the correct answer: A closed bottle containing water at 300°C is carried to the moon in a spaceship. If it is placed on the surface of the moon, what will happen to the water as soon as the lid is opened?

It will decompose into H₂ and O₂

Water will boil

Water will freeze

None of these

Explanation

On the moon, there is no atmospheric pressure, which lowers the boiling point of water.

Since the water is at 300°C, it will immediately boil once the lid is opened.

Q1678: Unequal expansion of metals makes possible the operation ____?

دھاتوں کی غیر مساوی توسیع آپریشن کو ____ ممکن بناتی ہے؟

Thermostats

Aneroid barometer

Hygrometers

None of these

Explanation

Thermostats work based on the unequal expansion of metals in a bimetallic strip.

This property helps in regulating temperature by switching devices on or off.

Q1679: In dry cell the electrolyte is a moist paste of ______?

خشک سیل میں الیکٹرولائٹ ______ کا نم پیسٹ ہے؟

NH4Cl and MnO2

NaCl and CuCl2

NH4Cl and ZnCl2

None of these

Explanation

In a dry cell, the electrolyte is a moist paste of ammonium chloride (NH₄Cl) and zinc chloride (ZnCl₂) to facilitate ion flow.

It helps in the movement of electrons between the zinc anode and the manganese dioxide cathode.

Q1680: Two vectors u,v are orthonormal if and only if?

Both u,v are orthogonal and unit vectors

u,v are orthogonal

u,v are unit vectors

None of these

Explanation

Orthonormal vectors satisfy two conditions: they are orthogonal ( $u cdot v = 0$ ) and unit vectors ( $||u|| = 1$ and $||v|| = 1$ .

This means they are perpendicular and have a magnitude of 1.

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