what is the mass of an atom that has 6 protons, 7 neutrons, and 6 electrons? 19 13 12 6

Explanation:

Step1: Recall mass - number formula

The mass number (A) of an atom is the sum of the number of protons (p) and neutrons (n). Electrons have negligible mass compared to protons and neutrons, so they are not considered in calculating the mass of the atom. The formula is $A=p + n$.

Step2: Identify values of p and n

Given that the number of protons $p = 6$ and the number of neutrons $n=7$.

Step3: Calculate the mass - number

Substitute the values into the formula: $A=6 + 7=13$.

Answer:

13