Answer
The corresponding particle is a Kaon $K^+$
Work Step by Step
The proton $p$ has strangeness $0$, charge $+1$, and baryon number $+1$
The $\Lambda^0$ has strangeness $-1$, charge $0$, and baryon number $+1$
The left side of the process has net strangeness $0$, net charge $+2$, and net baryon number $+2$
The $p$ and the $\Lambda^0$ on the right side of the process have net strangeness $-1$, net charge $+1$, and net baryon number $+2$
According to the conservation laws, the $x$ must have strangeness $+1$, charge $+1$, and baryon number $0$
The corresponding particle is a Kaon $K^+$
