Answer : (d) 225

Explanation : $\;A=\large\frac{25+n}{2}$

$G=\sqrt{25n}=5\;\sqrt{n}$

$H=\large\frac{50n}{25+n}$

For A to be natural , n must be odd

For G to be natural n must be a square

Now H wii be natural number

Only if n=225 (All other choices fails).