J.J. Thomson is credited with the discovery of: MCQ with Answer and Explanation

J.J. Thomson is credited with the discovery of:
A. Nucleus
B. Electron
C. Proton
D. Neutron
Answer: Option B
Solution (By JKSSB Mock Tests)
Thomson used cathode ray tubes to discover the electron and measure its charge-to-mass ratio (e/m). He proposed the 'plum pudding' model. Proton identified by Rutherford, neutron by Chadwick.

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Gamma rays are produced from:
A. Outer electron transitions
B. Nuclear de-excitation
C. Friction
D. Chemical reactions

Correct Answer: Option B


Explanation:
Gamma rays are high-energy photons emitted from the nucleus when it transitions from excited state to lower energy state. Alpha/beta decay often leaves nucleus in excited state which emits gamma.

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Sodium carbonate is a salt of:
A. Weak acid and strong base
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D. Weak acid and weak base

Correct Answer: Option A


Explanation:
Na₂CO₃ is formed from NaOH (strong base) and H₂CO₃ (weak acid). Its aqueous solution is basic due to hydrolysis: CO₃²⁻ + H₂O ⇌ HCO₃⁻ + OH⁻. Strong acid + strong base salts are neutral (NaCl).

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Correct Answer: Option B


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