For a reaction of the type $A P$ , the half-life is $80 min$ when $[A]_{0} = 0.10 mol L^{- 1}$ and $40 min$ when $[A]_{0} = 0.20 mol L^{- 1}$ . The order of the reaction is

Answer: D

Since

t_{1/2} \propto [A]_{0}^{1 - n}

, doubling

[A]_{0}

halves

t_{1/2}

, so

2^{1 - n} = 1/2

, giving

1 - n = - 1

and

n = 2

. For zero order the half-life would double, and for first order it would not change.