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JEE Advanced levelSingle correct optionDifficulty 3 of 3ck048

A reaction of zero order has a half-life of $25 min$ at $[A]_{0} = 0.50 M$ . The time needed for $[A]$ to fall from $0.50$ to $0.10 M$ is

A $58 min$
B $50 min$
C $40 min$
D $10 min$

Answer: C

For zero order

t_{1/2} = [A]_{0} /2 k

, so

k = 0.50/ (2 \times 25) = 0.010 M mi n^{- 1}

. The fall of

0.40 M

then takes

t = 0.40/0.010 = 40 min

. The value 58 min would come from wrongly applying first order kinetics.

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