The discovery of neutron became very late because ::

Question

$\begin{array}{1 1}(a)\;It\; is\; present\; in \;nucleus.\\(b)\;It\;is\; a\; fundamental\; particle.\\(c)\;It\; does\; not\; move. \\(d)\;It\; does\; not\; carry\; any \;charge.\end{array}$