Assertion (A): The mass of an atom is concentrated in the nucleus. Reason (R): Protons and neutrons are present inside the nucleus. MCQ with Answer and Explanation
Assertion (A): The mass of an atom is concentrated in the nucleus. Reason (R): Protons and neutrons are present inside the nucleus.
A. A is true but R is false.
B. A is false but R is true.
C. Both A and R are true and R is the correct explanation of A.
D. Both A and R are true but R is NOT the correct explanation of A.
Answer: Option C
Solution (By JKSSB Mock Tests)
The mass of an atom is almost entirely concentrated in its tiny central nucleus. This is because the nucleus contains protons and neutrons, which are much heavier than the extranuclear electrons. Since electrons have negligible mass, R correctly explains why the mass is localized in the nucleus.
Explanation:
Fractional distillation is used when the boiling points differ by less than 25 K. A fractionating column provides repeated condensation–vaporization cycles, improving separation. Example: separation of petrol, kerosene from crude oil. Simple distillation works if difference > 25 K. Separating funnel separates immiscible liquids. Crystallization purifies solids. Exam note: Fractionating column packed with glass beads increases surface area.
Explanation:
Cobalt-60 emits gamma rays used in radiotherapy to destroy cancerous cells. Carbon-12 and sodium-23 are stable. Phosphorus-32 is radioactive but used as tracer, not for cancer therapy.
Explanation:
Sodium carbonate is a salt of strong base (NaOH) and weak acid (H₂CO₃). On hydrolysis, it gives OH⁻ ions: CO₃²⁻ + H₂O ⇌ HCO₃⁻ + OH⁻, making the solution basic. pH ~11. It turns red litmus blue. It is used for softening hard water and in detergents. NaHCO₃ solution is also mildly basic. Salts of strong acid + strong base are neutral (NaCl). Salts of weak base + strong acid are acidic (NH₄Cl).
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