c
\({PCl}_{5}({~g}) \frac{1 \text { order }}{300 {~K}} {PCl}_{3(g)}+{Cl}_{2(g)}\)

\({t}=0 \quad\quad\quad\quad 50 {M}\)

\({t}=120 \min \quad10 {M}\)

\(\Rightarrow \quad {K}=\frac{2.303}{{t}} \log \frac{\left[{A}_{0}\right]}{\left[{A}_{{t}}\right]}\)

\(\Rightarrow \quad {K}=\frac{2.303}{{t}} \log \frac{50}{10}\)

\(\Rightarrow \quad {K}=\frac{2.303}{120} \times 0.6989=0.013413 \,{~min}^{-1}\)

\(= 1.3413 \times 10^{-2}\, {~min}^{-1}\)

\(1.34 \Rightarrow \text { Nearest integer }=1\)