Answer:

Explanation:
Assuming that all caculations are at normal pressure and -1.72°C :

Where
is the number of moles of hydrogen
is the mass of hydrogen
is the density of hydrogen
Answer:
alkali metals
Explanation:
they all react vigorously or even explosively with cold water, resulting in the displacement of hydrogen.
Answer:
D
Explanation:
Firstly it is pertinent to know that, Electric force are due to the movement of electrons that is due to its gain and loss. This phenomenon is based on static electricity.
When the glass ruler is rubbed over the woolen sweater, the wool gets positively charged and the ruler gains electron to form negative charge.
Now if this charged is not earthed, the negative charged ruler attracts the uncharged bits of paper, as a result of which the paper gets attached to the ruler.