1)

There is a similar worked example in HC Verma in page no. 93 Q.no.12

 

Do have a look at it and tell me if you have any doubts

 

6)

Use Charles and volume V=AL

 

Here V₁=50A  T₁=300K    V₂=XA     T₂=384K    where A is area of cross section

 

Using V₁/T₁=V₂/T₂

 

We get X=64cm

 

So the mercury level falls by 14cm