Question

consider the nuclear equation.
239 94 pu→x+4 2 he
what is x?
243 92 u
235 92 u
235 96 cm
243 96 cm

Explanation:

Step1: Calculate the mass number of \( X \)

In a nuclear reaction, the sum of mass numbers on the left - hand side equals the sum of mass numbers on the right - hand side.
The mass number of \( ^{239}_{94}Pu \) is \( A_{Pu}=239 \), and the mass number of \( ^{4}_{2}He \) is \( A_{He} = 4 \).
Let the mass number of \( X \) be \( A_X \). Then \( A_{Pu}=A_X + A_{He} \), so \( A_X=A_{Pu}-A_{He}=239 - 4=235 \).

Step2: Calculate the atomic number of \( X \)

The sum of atomic numbers on the left - hand side equals the sum of atomic numbers on the right - hand side.
The atomic number of \( ^{239}_{94}Pu \) is \( Z_{Pu}=94 \), and the atomic number of \( ^{4}_{2}He \) is \( Z_{He}=2 \).
Let the atomic number of \( X \) be \( Z_X \). Then \( Z_{Pu}=Z_X+Z_{He} \), so \( Z_X=Z_{Pu}-Z_{He}=94 - 2 = 92 \).

Step3: Identify the element

The element with atomic number \( Z = 92 \) is Uranium (\( U \)).

Answer:

\( ^{235}_{92}U \)