The gas used in the hydrogenation of oils in the presence of nickel as a catalyst is

The sum of the number of protons and neutrons in all isotopes of hydrogen is .......

What is believed to be the second most common element in the universe?

Which of the following is used for the extraction of glue from bones?

Which property among the following is the same for both hydrogen and deuterium molecules?

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.