It's 1 because there is only one electron on the outer shell.
Answer:
ELEMENTS MIXTURE
Elements are made up of one kind of atoms. Mixtures are made up of two or more kinds of Compounds .
Elements cannot be broken down into simpler substances by any physical or chemical method. The various constituents are seperated by simple physical means
Boyle's law states that pressure is inversely proportional to volume of gas at constant temperature
PV = k
where P - pressure , V - volume and k - constant
P1V1 = P2V2
where parameters for the first instance are on the left side and parameters for the second instance are on the right side of the equation
substituting these values in the equation
1.25 atm x 0.75 L = P x 1.1 L
P = 0.85 atm
final pressure is B) 0.85 atm
