Combustion of octane takes place in an automobile engine.The homogeneous equation of combustion is :${\mathrm{C}}_8{\mathrm{H}}_{18}+\frac{25}{2}{\mathrm{O}}_2\to 8 {\mathrm{CO}}_2+9 {\mathrm{H}}_2\mathrm{O}$

the sign of $∆\mathrm{G}$ for the reaction will be :

Match List-I with List-II :

Choose the correct match :

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R 

Assertion A: Hydrogen is an environment friendly fuel.

Reason R: Atomic number of hydrogen is $1$ and it is a very light element.
In the light of the above statements, choose the correct answer from the options given below

Give reason for the following:

Hydrogen gas can prevent pollution.