The unit of 1 atmosphere used to describe the pressure of a gas is equal to 760 mm hg. 200 mm hg. 600 mm hg. 100 mm hg. 1 mm hg.

Answer is 1 atm = 760 mm Hg.

There are many units which are used to measure the pressure. Examples are atm, Pascal (Pa), torr, mm Hg and bar.
Although there are many units, the SI unit is Pascal (Pa). The relationship between those units as follows;

1 atm = 101325 Pa = 1.01325 bar = 760 mm Hg = 760 torr.

Ithink the answer is 56.