Identify catalyst used in manufacturing of HDP.

Air is an example of a solution of

A gas has a volume of $$3.4 \mathrm{~L}$$ at $$298 \mathrm{~K}$$. What is the final temperature if the volume of gas increases to $$6.8 \mathrm{~L}$$ ?

What is the atomic radius of polonium if it crystallises in a simple cubic structure with edge length of unit cell $$336 \mathrm{~pm}$$ ?