Describe the structure of diborane.

Explain the following reaction:
Silicon is heated with methyl chloride at high temperature in the presence of copper.
 

Give reason why graphite is used as a lubricant?

Give reason why diamond is used as an abrasive?

How do the following property vary when we move from carbon to lead in group $14$?

Atomic radius

${\mathrm{B}}_2{\mathrm{H}}_6\underset{\mathrm{Sealed} \mathrm{tube}}{\overset{373 \mathrm{K}}{\to }} ?$

Complete the above reaction.