Answer:
For any given isotope, the sum of the numbers of protons and neutrons in the nucleus is called the mass number. This is because each proton and each neutron weigh one atomic mass unit. By adding together the number of protons and neutrons and multiplying by 1, you can calculate the mass of the atom.
Explanation:
temperature changes affect seawater density as water cools its density increases. As water cools H2O molecules pack more closely together because the molecules are vibrating less at low temperatures and take up less volume. The same number of water molecules in smaller volume results higher density

is aluminium oxide (also called aloxide, aloxite and alundum). It is neither acid nor base. It has amphoteric nature meaning it can act as an acid with bases and as a base with acids. It neutralises them to salts.
The answer is (C) as the definitions states that atomic mass is the number of protons and neutrons.
Hope this helps :).