The maximum sum of the number of neutrons and protons in an isotope of hydrogen is

Which of the following is an example of an interstitial hydride?

Which element does not contain any neutrons?

Pure dihydrogen $(99.95\%)$ is obtained by the electrolysis of

Which of the following combinations represents water gas?

How many of the following statements is/are correct?
$(a)$ Mercury is the only metal that exists as liquid at room temperature.
$(b)$ Among non-metals,carbon has the highest melting point.
$(c)$ Hydrogen is the most abundant element in the universe.
$(d)$ Oxygen is the most abundant element in the earth's crust.