70.306 would be your answer.
Explanation
NaCl: Ionic crystal lattice forces
Hg: Metallic bonding
CO₂: London dispersion forces
CH₄: London dispersion forces
Li₂O: Ionic crystal lattice forces
Ag: Metallic bonds
Ionic crystal lattice forces are strong electrostatic force of attraction between oppositely charged ions arranged into a crystal lattice of ionic compound. NaCl and Li₂O are ionic compounds
London dispersion forces holds the molecules of carbon dioxide and methane. They are weak attractions found between non-polar (and polar) molecules.
Metallic bonds exists between Mercury and Gold atoms. This is due to sea of electrons present.
Here we go ~
1 mole of 
has 6.022 × 10²³ molecules of the given compound.
So, 0.78 mole of 
will have ~
Answer: The correct option is (c). The total pressure doubles.
Solution:
Initially, only 4 moles of oxygen gas were present in the flask.
(
) ( according to Dalton's law of partial pressure)
....(1)
= Total pressure when only oxygen gas was present.
Final total pressure when 4 moles of helium gas were added:
partial pressure of oxygen in the mixture :
Since, the number of moles of oxygen remains the same, the partial pressure of oxygen will also remain the same in the mixture.
= Total pressure of the mixture.
from (1)
On rearranging, we get:
The new total pressure will be twice of initial total pressure.
1,2-methylcyclohexane, 1,3-methylcyclohexane, 1,4-methylcyclohexane
