Asample of helium, at 20 °c, occupies a volume of 3.17 l at a pressure of 6.21 atm. what volume does this helium sample occupy if the pressure is reduced to 5.57 atm while maintaining the temperature at 20 °c?

Boyle's law gives the relationship between pressure of a gas and volume.
It states that at a constant temperature the pressure of gas is inversely proportional to volume of gas.
PV = k
where P - pressure, V - volume and k - constant
P1V1 = P2V2
where parameters for the first instance are given on the left side and parameters for the second instance are given on the right side of the equation.
substituting these values in the equation
6.21 atm x 3.17 L = 5.57 atm x V
V = 3.53 L
new volume is 3.53 L

A.

Outermost (valence) electrons