# Heavy water molecule made from $_1 H ^3$ and $_8 O ^{18}$ has a mol.wt of

$(a)\;18\qquad(b)\;20\qquad(c)\;22\qquad(d)\;24$

$H_2^3O^{18};$ mol weight =$2\times 3+18=24$
Hence (d) is the correct answer.