The half-life of Iodine-131 is 8 days. If a sample has initial activity of 100 counts per minute, after 24 days the activity will be: MCQ with Answer and Explanation
The half-life of Iodine-131 is 8 days. If a sample has initial activity of 100 counts per minute, after 24 days the activity will be:
A. 12.5
B. 50
C. 25
D. 6.25
Answer: Option A
Solution (By JKSSB Mock Tests)
Number of half-lives = 24/8 = 3. Fraction remaining = (1/2)³ = 1/8. Activity = 100 × 1/8 = 12.5 counts per minute. Radioactive decay is exponential. After 1 half-life: 50, 2: 25, 3: 12.5. This isotope is used in thyroid treatment.
Explanation:
Sodium carbonate decahydrate (washing soda) is prepared by dissolving soda ash (anhydrous Na₂CO₃) in water and allowing it to crystallise. Heating would remove water of crystallization (efflorescence). Adding acid would decompose it. Electrolysis would produce NaOH and Cl₂ from brine, not washing soda directly.
Explanation:
Acids turn blue litmus red; bases turn red litmus blue. Litmus is a purple dye extracted from lichens, used as an indicator. pH < 4.5 red, > 8.3 blue, intermediate purple. Neutral solution (pH 7) does not change the color of litmus significantly. This is a simple test for acid-base nature.
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