Question

what is the mass number of a carbon isotope that has seven neutrons?
a 13
b 11
c 7
d 9

Explanation:

Step1: Recall carbon's proton number

Carbon has 6 protons.

Step2: Use mass - number formula

Mass number = number of protons+number of neutrons. Given 6 protons and 7 neutrons, mass number = 6 + 7.

Step3: Calculate the mass number

6+7 = 13.

Answer:

A. 13