# If $P(2,3,4)\;and\:Q(1,b,1)$ are two points and $O$ is origin such that $OP$ is $\perp$ to $OQ$, then $b=?$
$(a)\:\:0\:\:\:\qquad\:\:(b)\:\:2\:\:\:\qquad\:\:(c)\:\:-2\:\:\:\qquad\:\:(d)\:\:No\:real\:value.$