Answer:
D.All of the above
Step-by-step explanation:
Properties of hydrogen:
1.It is lighter than air.It has density about 0.089 g/L.
2.Hydrogen rapidly change from liquid state to gas,so special protection is required to protect it.
3.It is highly flammable gas.
4.Liquid form of hydrogen exits at -432 F .This is very low temperature so special protection requires to keep it in liquid form.