Question

multiple choice question
hydrogen has an atomic weight of 1amu and oxygen has an atomic weight of 16amu. what is the molecular weight of water (h₂o)?
32amu
2amu
12amu
18amu

Explanation:

Step1: Calculate hydrogen's contribution

There are 2 hydrogen atoms in $H_2O$, and each hydrogen has an atomic weight of 1 amu. So the total weight of hydrogen is $2\times1$ amu = 2 amu.

Step2: Add oxygen's weight

Oxygen has an atomic weight of 16 amu in $H_2O$.
The molecular weight of $H_2O$ is the sum of the weights of hydrogen and oxygen, so it is $2 + 16$ amu = 18 amu.

Answer:

18amu (corresponding to the last option in the multiple - choice list)