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 don't really understand what you asking in this question so if you don't mind plz tell me in a better form
Any property that is measurable, whose value describes a state of a physical system.
double displacement
bcoz each of the reactants combines with other reactants to obtain the product
Answer: The first one is your answer. (If two people pull on it in opposite directions, it stretches. Then when they let it go, it returns to its original size and shape.)