In the nuclear reaction ${ }_{92} U^{238} \rightarrow {}_z T h^A+{ }_2 \mathrm{He}^4$, the values of A and Z are

A = 234, Z = 94 A = 234, Z = 90 A = 238, Z = 94 A = 238, Z = 90

A = 234, Z = 90

A = 238 – 4 = 234 and Z = 92 – 2 = 90.