Complete the following equations 
\(PbS(s)+{ H }_{ 2 }{ O }_{ 2 }(aq)\)

2

(a)

Basic principle of hydrogen economy is transporation and storage of energy in the form of liquid or gaseous hydrogen.Which property of hydrogen may be usefuk for this chemical equation if required.

2

(a)

Give reasons.
Lakes freeze from top towards bottom

2

(a)

Give reasons.
Ice floats on water

2

(a)

Explain why HCl is a gas and HF a liquid?

2

(a)