Solution

2) On the right is a graph showing the boiling points of the group 4,5,6 and 7 hydrides. For the most part the trend is exactly the same in all four groups except that the boiling point of the compound of hydrogen with the first element in group 4 is abnormally low.

Why?

i. Methane (CH4)  does not exhibit hydrogen bonding between its molecules as does NH4, H2O and HF.

ii. The Intermolecular forces are weaker in methane as it not only has no hydrogen bonding but its dispersion forces are also weaker due to the fact it is a smaller molecule than HF,  NH4 and H2O.

 

The polarity of the bonds formed when hydrogen bonds with oxygen, nitrogen or fluorine is much greater than the polarity of the bond formed between hydrogen and carbon.

 
Such strong poles create relatively strong intermolecular forces of attraction known as hydrogen bonding.
Also, methane is a symmetrical molecule and hence has no dipoles. In other words it does not have two opposite charged ends as the delta minus charge in the middle is surrounded by the delta positive charges. This makes for very weak forces of attraction and so methane has a very low boiling temperature.