Question

what is most likely true of an atom with a mass of 15 amu? there are 15 protons. there are 15 electrons. the total number of protons and electrons is 15. the total number of protons and neutrons is 15.

Explanation:

Step1: Recall atomic - mass formula

The atomic mass (in amu) of an atom is approximately equal to the sum of the number of protons and neutrons in the nucleus of the atom, i.e., $Atomic\ mass = Number\ of\ protons+Number\ of\ neutrons$.

Step2: Analyze each option

• Option 1: Just having 15 protons is incorrect as atomic mass is sum of protons and neutrons, not just protons.
• Option 2: Electrons have negligible mass compared to protons and neutrons, so number of electrons does not determine atomic mass.
• Option 3: Protons and electrons are not related to atomic - mass calculation in this way.
• Option 4: This is consistent with the formula for atomic mass.

Answer:

The total number of protons and neutrons is 15.