Plastics are polymers that can be molded when heated. Which of the following is a thermosetting plastic?
A. Bakelite
B. Polyethylene
C. Nylon
D. PVC
Answer: Option A
Solution (By JKSSB Mock Tests)
Bakelite is a thermosetting plastic (phenol-formaldehyde resin). Once set, it cannot be remolded by heating because its polymer chains are cross-linked. Polyethylene, PVC, and nylon are thermoplastics—they can be repeatedly softened by heat and hardened on cooling. Thermosetting plastics are used for electrical switches, handles, and adhesives. Vulcanized rubber is also thermoset.
Explanation:
Water (H₂O) is a compound – a pure substance composed of two or more elements chemically combined in a fixed ratio. Oxygen is an element. Air is a mixture of gases. Steel is an alloy (mixture). Compounds can be broken down by chemical methods.
Explanation:
Soap is made by saponification: fat/oil (triglyceride) + NaOH → glycerol + sodium salt of fatty acid (soap). This is an alkaline hydrolysis. HCl would break down differently. NaCl is used to precipitate soap (salting out). Ethanol is solvent.
Explanation:
Number of half-lives = total time / half-life = 10/5 = 2. Fraction remaining = (1/2)ⁿ = (1/2)² = 1/4. Thus 25% remains. After 3 half-lives (15 years) it would be 1/8.
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