Question

multiple choice 2 points
what is the atomic number of the missing element (the number of protons)?
235 92u + 1 0n → 95 37rb + □ + 2·1 0n
137 139 141 140
multiple choice 1 point
for the following equation, what is the mass of the missing element?
235 92u + 1 0n → 95 37rb + □ + 2·1 0n

Explanation:

Step1: Calculate the mass of the missing element

In a nuclear reaction, the sum of the mass numbers on the left - hand side equals the sum of the mass numbers on the right - hand side.
The mass number of \(_{92}^{235}U\) is \(235\), the mass number of \(_{0}^{1}n\) is \(1\), the mass number of \(_{37}^{95}Rb\) is \(95\), and the mass number of \(2\cdot_{0}^{1}n\) is \(2\times1 = 2\).
Let the mass number of the missing element be \(x\). Then \(235+1=95 + x+2\).
Simplify the equation: \(236=97 + x\).
Solve for \(x\): \(x=236 - 97=139\).

Step2: Calculate the atomic number of the missing element

The sum of the atomic numbers on the left - hand side equals the sum of the atomic numbers on the right - hand side.
The atomic number of \(_{92}^{235}U\) is \(92\), the atomic number of \(_{0}^{1}n\) is \(0\), the atomic number of \(_{37}^{95}Rb\) is \(37\), and the atomic number of \(2\cdot_{0}^{1}n\) is \(2\times0 = 0\).
Let the atomic number of the missing element be \(y\). Then \(92+0 = 37+y + 0\).
Solve for \(y\): \(y=92 - 37=55\).

Answer:

The mass number of the missing element in the first reaction (related to the mass calculation) is \(139\).