For a random variable $X$ if $P(X=k)=\frac{(k+1) a}{3^k}$ for $k=0,1,2, \ldots$ then $a=$

• A

  $\frac{2}{3}$
• Correct answer
  B

  $\frac{4}{9}$
• C

  $\frac{8}{27}$
• D

  $\frac{16}{81}$

Hence, the correct answer is option: 'B'.