LCM of $36$ and $72$ is:

The correct option is B $72$
First find the factors of both the numbers.

$36=2\times 2\times 3\times 3$

$72=2\times 2\times 2\times 3\times 3$

Hence,

$LCM(36,72)=2\times 2\times 2\times 3\times 3$

$=8\times 9$

$=72$

Hence, the answer is $72$.