Number of protons, neutrons and electrons in the element \[_{89}X^{231}\] is
a) 89, 89, 242
b) 89, 142, 89
c) 89, 71, 89
d) 89, 231, 89

Answer: b
Explanation: Number of p = number of e^– = 89 and neutrons 231 – 89 = 142.