Question

b. sulfur - 34 (z = 16)

Explanation:

Step1: Recall the relationship between mass - number, atomic number and neutrons

The mass - number (A) of an isotope is given, and the atomic number (Z) is given. The number of neutrons (N) is calculated by the formula $N=A - Z$.
For sulfur - 34, the mass - number $A = 34$ and the atomic number $Z=16$ (since for sulfur, $Z = 16$).

Step2: Calculate the number of neutrons

Substitute the values into the formula: $N=34 - 16$.
$N = 18$.

Answer:

18