Answer
a) 31
b) 143
c) 25
d) 24
Work Step by Step
a) Number of neutrons (n) = Mass number (A)-Atomic number (Z).
Given A = 59 and Z = 28. Then, $n = 59-28 = 31.$
b) $n= A-Z = 235-92 = 143$
c) In this case, A= 46 and Z = 21.
$n= 46-21 = 25$
d) Here, Z = 18, A = 42.
$n = A-Z = 42-18 = 24$
