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

The scientist who proposed the first letter (or first letter and another letter) of the Latin or English name of an element as its symbol, was:

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

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

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