What is the Mr of a water molecule (H2O)?

To calculate the molecular mass (Mr) of a water molecule (H2O), you need to know the atomic masses of hydrogen (H) and oxygen (O).

1. The atomic mass of hydrogen (H) is approximately 1.
2. The atomic mass of oxygen (O) is approximately 16.

In a water molecule, there are 2 hydrogen atoms and 1 oxygen atom.

So, you calculate the molecular mass as follows:

(2 * atomic mass of hydrogen) + (1 * atomic mass of oxygen)

= (2 * 1) + (1 * 16)

= 2 + 16

= 18

So, the molecular mass (Mr) of a water molecule (H2O) is 18.