In water, the proportion of oxygen and hydrogen by mass is:

The atoms of which of the following pair of elements are most likely to exist in free state?

Which of the following elements has the same molecular mass as its atomic mass?

In hydrogen peroxide (H₂O₂), the proportion of hydrogen and oxygen by mass is:

The symbols of the elements cobalt, aluminium, helium and sodium respectively written by a student are as follows. Which symbol is the correct one?