Nuclear fission equation $\begin{aligned}
{ }{92} \mathrm{U}^{135}+{ }0 \mathrm{n}^1 \longrightarrow & { }{56} \mathrm{Ba}^{141}+{ }{36} \mathrm{Kr}^{92} \
& +3{ }_0 \mathrm{n}^1+\mathrm{Q}(\text { energy })
\end{aligned}Henceparticle\mathrm{x}$ is neutron.