The Concentration of Carbon Monoxide in a Sample of Air

The concentration of carbon monoxide in a sample of air is 6.0 ppm. There are ________ molecules of CO in 1.00 L of this air at 755 torr and 23 °C.

A) 2.5 × 10^-7
B) 1.4 × 10²¹
C) 1.9 × 10¹⁸
D) 1.1 × 10²⁰
E) 1.5 × 10¹⁷