\\\\(_{4}Be^{9} + _{2}He^{4} \\rightarrow _{6}C^{12} + X\\\\)No. of protons are already balanced with \\\\(C\\\\).\\\\(\ herefore\\\\) \\\\(X\\\\) carries no charge.and \\\\( 9+4 > 12\\\\) by \\\\(1\\\\) unit mass.\\\\(\ herefore\\\\) \\\\(X\\\\) carries one unit mass.It's a neutron.