The volume of a gas is 400.0 ml when the pressure is 1.00 atm. at the same temperature, what is the pressure at which the volume of the gas is 2.0 l? a. 0.5 atm b. 5.0 atm c. 0.20atm d. 800 atm

The question mentions a change in volume from 400 mL to 2L, which is accompanied by a change in pressure from 1 atm. Therefore, the premise of this question is Boyle's Law, which notes that pressure is inversely proportional to volume at constant temperature (as volume increases, pressure decreases, and vice versa). As such, Boyle's Equation can be used to determine the final pressure of the air. 

Boyle's Equation:      P₁V₁    =    P₂V₂
Since the initial volume (V₁) is 400 mL =  0.4 L, the final volume (V₂) is 2L and the initial pressure is 1 atm, then we can substitute these into the equation to find the initial volume (V₁).

                                                  P₁V₁    =    P₂V₂
∴ by substituting the known values,                               
                     ⇒     (1 atm) (0.4 L)  =  (P₂)(2 L)                                                              
                     ⇒                       P₂  =  (0.4 atm L) ÷ ( 2 L)                                     
                     ⇒                       P₂  =  0.2 atm

Thus the answer is 0.20 atm (option C)

Answer two atoms of oxygen;