Consider the nuclear equation. 94 to the 239th power Pu rightarrow cap x plus 2 to the 4th power He What is X ?

Conserve both the mass number and the atomic number in the nuclear equation. The helium nucleus has mass number 4 and atomic number 2, so X must have mass number 239 − 4 = 235 and atomic number 94 − 2 = 92. The element with atomic number 92 is uranium, so X is uranium-235, choice A.

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