Question One
It's more a question of unscrambling what is there. The answer is correct.
If you look at your periodic table, there is such an element as Na which I suspect might be the problem.
It has an atomic mass of 23. It's atomic number is 11 which means it is the 11th member (by mass) on the periodic table. The other 2 are oxygen and hydrogen. So Oxygen has an atomic mass of 16 and Hydrogen has an atomic mass of 1.
Oxygen is number 8 on the periodic table and hydrogen is number 1.
Molecular Mass
Na = 23
O = 16
H = 1
Total 40, just as the answer key says. I've probably given you more than you wanted to know, but if you still have trouble, leave a note.
