Answer : The amount of formaldehyde permissible are, 
Explanation : Given,
Density of air =

First we have to calculate the mass of air.



Now we have to calculate the amount of formaldehyde.
Permissible exposure level of formaldehyde = 0.75 ppm = 
Amount of formaldehyde in 7.2 g of formaldehyde = 
Amount of formaldehyde in 7.2 g of formaldehyde = 
Thus, the amount of formaldehyde permissible are, 
Answer:
I think b is the correct answer
An extra shell, which means further distance between those electrons in the valence shell and the nucleus. Ionisation energy refers to the energy required to remove valence electrons. There will be more energy required if the valence electrons are closer to the nucleus that have a positive charge, because of more attraction. If there is an extra shell, there is further distance, less attraction and hence less energy required.