The length of a side of a square whose area is $441$ sq cm is

The correct option is A: $21$ cm

Area of square $=441$ sq cm

We know that Area of square $=(side{)}^2$

Thus, $(side{)}^2=441$

$\Rightarrow (side{)}^2=(21{)}^2$

$\begin{array}{cc}3& 441\\ 3& 147\\ 7& 49\\ 7& 7\\ & 1\end{array}$

Then, side $=21$ cm

$441=3\times 3\times 7\times 7$

$441=21\times 21={21}^2$