what is the mass of this atom?

Explanation:

Step1: Identify particles in nucleus

Protons (red) and neutrons (green) contribute to mass. There are 3 protons and 4 neutrons.

Step2: Recall mass - particle relationship

Protons and neutrons each have a mass of approximately 1 atomic mass unit (amu).

Step3: Calculate atomic mass

Add number of protons and neutrons: $3 + 4=7$ amu.

Answer:

7 amu