Answer: 17) d. 
18. c. The empirical formula of a compound can be twice the molecular formula.
Explanation:
Molecular formula is the chemical formula which depicts the actual number of atoms of each element present in the compound.
Empirical formula is the simplest chemical formula which depicts the whole number of atoms of each element present in the compound.
To calculate the molecular formula, we need to find the valency which is multiplied by each element to get the molecular formula.
The equation used to calculate the valency is:

The empirical mass can be calculated from empirical formula and molar mass must be known.
17. Thus the empirical formula of
should be 
18. The molecular formula will either be same as empirical formula or is a whole number multiple of empirical formula. Thus the empirical formula of a compound can never be twice the molecular formula.
Second law of thermodynamics states entropy of the universe is always increasing. entropy always increases in a spontaneous process .
option B) second law of thermodynamics
for example if we keep a hot cup of coffee the heat is lost to surrounding and entropy( randomness increases) since it is a natural process entropy of universe increases.
Gibbs free energy of a reaction (
Δ
G ) is the change in free energy of a system that undergoes the chemical reaction. It is the energy associated with the reaction, which is available to do some useful work. If ΔG<0
, then the reaction can be utilized to do some useful work. If
ΔG>0
, then work has to be done on the system or external energy is required to make the reaction happen. ΔG=0 when the reaction is at equilibrium and there is no net change taking place in the system.
The kinetic energy causes the air molecules to move faster and they impact the container walls more frequently and with more force. The kinetic energy of the gas molecules increases, so collisions with the walls of the container are now more forceful than they were before. As a result, the pressure of the gas doubles.