Answer: $B$. 2250
Let $l$ and $b$ be the length & breadth of rectangle.
Area of rectangle, $A = l\times b \qquad \to (1)$
Given, rectangle becomes square when $l$ reduces by $10$ and $b$ reduces by $5$
$\implies l-10 = b-5\qquad \to (2)$
Then, area of square $= (l-10)\times (b-5) = A-650$
$\implies (l-10)\times(b-5) = (l\times b) - 650 \qquad \to (3)$
Solving, $(ii)$ & $(iii)$ we get $b=45,l=50.$
Thus, area of rectangle $= 45\times 50 = 2250\;m^2$