If the atomic number of an element is 6 and its mass number is 13, how many neutrons are
contained in the nucleus?
19
8
7
6

There will be 7 neutrons in a carbon isotope with an atomic mass of 13.

Explanation:

The number of protons in the carbon isotope will be the same as the atomic number, 6, so if we need an atomic mass of 13 there will be 7 neutrons, as 6+7=13.

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.