Is columns of elements in the periodic table are called periods correct in the underlined sentence

Agas diffuses 1/7 times faster than hydrogen gas (h2). what is the molar mass of the gas? 100.10 g/mol 98.78 g/mol 86.68 g/mol 79.98 g/mol

Agas can holds 2.0 gal of gasoline. what is this quantity in cubic centimeters?

The climate of the continental united states is generally 1. tropical 2. temperate 3. arctic 4. highland