The mass per volume of a substance is called its density.
The relationship between the evaporation rate and the likelihood that the liquid will be flammable is its flash point number (or the lowest temperature for which the liquid ignites) and its activation energy (how much energy is required to ignite it). With volatile liquids or gases these numbers seem to be lower.
Answer :
(a) The number of moles of D produced can be, 6.67 moles.
(b) The volume of D prepared can be, 24.5 L
Explanation :
The given chemical reaction is:

Part (a) :
From the balanced chemical reaction, we conclude that:
As, 3 moles of A react to give 5 moles of D
So, 4 moles of A react to give
moles of D
Thus, the number of moles of D produced can be, 6.67 moles.
Part (b) :
As we know that 1 moles of substance occupies 22.4 L volume of gas.
As,
volume of B gives
volume of D
As, 9.8 L volume of B gives
volume of D
Thus, the volume of D prepared can be, 24.5 L