Consider the following first order decomposition reaction $A_4\left(g\right)\to 4A\left(g\right)$
 Correct statements regarding the reaction . $[\log 2=0.3]$
 

   $A_4\stackrel{}{\to }4A$
  $t=0$ am   0
$t=30$  $(a-x)m$   $4xm$              
As                $a-x=4x$     $x=a/5$
Percentage $r\times n$  at  $t=30\min$
 $=\frac{x}{a}\times 100=20\%$
Now,  $30=\frac{t_{1/2}}{\log 2}.\log \frac{a}{a-x}\Rightarrow t_{1/2}=90\min$