a
Let the side length of the square park is 1 . The area of a square is given as,
$A=1^2$
$100=1^2$
$1=10\,m$
The error in length is given as,
$\frac{\Delta A }{ A }=2 \frac{\Delta l }{1}$
$\frac{0.2}{100}=2 \frac{\Delta l }{10}$
$\Delta l =0.01\,m$
Thus, the side of the park is $(10 \pm 0.01)\,m$.