Dihydrogen

What is the third most abundant element on the surface of the earth?

Why does hydrogen exist as a diatomic molecule while all alkali metals exists as monoatomic molecules?

 Why hydrogen is more electronegative than sodium?

Why is the ionisation enthalpy of hydrogen higher than that of sodium?

Compare hydrogen with alkali metals on the basis of size of the ions.

Compare hydrogen with alkali metals on the basis of nature of compounds.

The position of which of the following elements is debatable?

The present position of hydrogen in the modern periodic table is completely justifiable.

Explain the reason behind controversial position of hydrogen in the periodic table.

Hydrogen is the third most abundant element in the globe. Then, why does hydrogen occupy unique position in the periodic table?

Give the abundance of hydrogen in the universe.

Consider the following statements.

(i) The most common isotope of hydrogen is protium.

(ii) Water-gas shift reaction is a multistep reaction.

(iii) ${\mathrm{D}}_2\mathrm{O}$ has a higher boiling point than ${\mathrm{H}}_2\mathrm{O}$.

Which of the above statements is/are true?

Radioactive elements emit $\mathrm{\alpha }, \mathrm{\beta }$ and x-rays are characterized by their half lives. The radioactive isotope of hydrogen is:

Hydrogen resembles halogens in many aspects for which several factors are responsible. Which one is the most important in this respect?

The most abundant element in the universe is:

Where can we found hydrogen in free state?

Which of the following orders is correct?
a. Order of percentage relative abundance is protium $>$ deuterium $>$ tritium.
b. Order of density is protium $<$ deuterium $<$ tritium.
c. Order of boiling point is protium $>$ deuterium $>$ tritium.
d. Order of atomic mass is protium $>$ deuterium $>$ tritium.

The most abundant element in the universe is:

_____ is the most abundant element in the universe.

What are the natural sources of hydrogen gas?