Isotopes differ in the number of: MCQ with Answer and Explanation

Isotopes differ in the number of:
A. Neutrons
B. Positrons
C. Electrons
D. Protons
Answer: Option A
Solution (By JKExamLibrary)
Isotopes are atoms of the same element with the same atomic number (protons) but different mass numbers due to varying number of neutrons. For example, protium (¹H) has 0 neutrons, deuterium (²H) has 1, tritium (³H) has 2. Chemical properties are nearly identical because electronic configuration is the same, but physical properties (mass, density) differ.

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Cement sets under water because of:
A. Oxidation
B. Polymerization
C. Evaporation
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Correct Answer: Option D


Explanation:
Cement sets by hydration reactions forming C-S-H gel and Ca(OH)₂, even underwater. It's a chemical process, not drying. Gypsum controls the setting rate.

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Rusting of iron is accelerated in:
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Correct Answer: Option C


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Glass is considered a:
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C. Molecular solid
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Correct Answer: Option B


Explanation:
Glass is an amorphous (non-crystalline) solid, sometimes called a supercooled liquid. It lacks long-range periodic order; atoms are arranged in a disordered network. It softens over a temperature range rather than having a sharp melting point. Common glass is soda-lime-silicate glass. Crystalline solids have sharp melting points and regular lattice structures (e.g., NaCl, quartz).

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