If $\;(2+i)(2+2i)(2+3i)....(2+ni)=x+iy\;$ , then$\;5\;.8\;.13....(4+n^{2})=$----

Question

$(a)\;x^{2}+y^{2} \qquad(b)\;x^{2}-y^{2} \qquad(c)\;2(x^{2}+y^{2}) \qquad(d)\;0$