<span>Answer:
Moles Ca(NO3)2 = 100 x 0.250 / 1000 = 0.025
Ca(NO3)2 >> Ca2+ + 2NO3-
Moles NO3- = 2 x 0.025 = 0.05
Moles HNO3 = 400 x 0.100 / 1000 = 0.04
Total moles = 0.05 + 0.04 = 0.09
Total volume = 500 ml = 0.500 L
M = 0.09 / 0.500 = 0.18</span>
The answer is D) a neutron.
When we say an atom's mass is, like 5 atomic mass units actually we are saying that the total number of the neutrons and protons in its nucleus is 5.
The mass of a neutron and a proton is each one atomic mass unit.
Mass of a neutron is approximately 1 atomic mass unit.