States of Matter — Chemistry

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States of Matter

3 questions

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Q.1

WBCS Prelims 2023

Two drops of liquid merge to form a single drop. In this process energy is

A. absorbed.

B. released.

C. may be absorbed or released depending upon the specific heat of the liquid.

D. neither absorbed nor released.

Explanation

Why Correct: Merging reduces total surface area, decreasing surface energy which releases energy as heat.
Distractor Analysis: Energy absorption occurs when surface area increases, like breaking a drop. Specific heat affects temperature change during energy release, not the direction. Surface energy always decreases during merging, making energy release inevitable.
Takeaway: Surface tension causes liquids to minimize surface area; any process reducing area releases surface energy proportional to surface tension coefficient.

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Q.2

WBCS Prelims 2003

If the density of air is 1.30 g/lit. what is the volume occupied by 7.8g of air?

A. 10 lit.

B. 6 lit.

C. 6.5 lit.

D. 10/10 lit

Explanation

Core Formula/Logic: Density = Mass ÷ Volume, so Volume = Mass ÷ Density.
Step-by-Step Solution: 1. Density = 1.30 g/lit, Mass = 7.8 g. 2. Volume = 7.8 ÷ 1.30 = 6 lit.
Common Pitfall: Dividing density by mass (1.30 ÷ 7.8 ≈ 0.167) gives no listed option. Multiplying mass and density (7.8 × 1.30 = 10.14) yields option A. Option D (10/10 = 1) results from misplacing decimal points or misreading the fraction.
Shortcut/Takeaway: For density problems, always use V = M/D. Check units: g ÷ (g/lit) = lit, confirming the calculation. When dividing decimals, align decimal points: 7.80 ÷ 1.30 = 6.

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Q.3

WBCS Prelims 2001

Glass is best described as

A. a gel

B. an alloy

C. a eutectic mixture

D. a supercooled solution

Explanation

Why Correct: Glass forms when a molten silica mixture cools too rapidly for crystals to form, resulting in an amorphous solid with liquid-like disordered molecular structure.
Distractor Analysis: Gels contain a continuous solid network with liquid trapped inside, like jelly. Alloys are homogeneous mixtures of metals, such as steel or brass. Eutectic mixtures have specific compositions that melt at a single temperature lower than any component alone, like solder.
Takeaway: Other amorphous solids include obsidian (volcanic glass) and many plastics, while crystalline solids like quartz have regular atomic arrangements.

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