Answer:
2.78 x 10²³
Explanation:
1 mole contains 6.02 x 10²³ hydrogen atoms => 0.46 mole contains 0.46(6.02 x 10²³) hydrogen atoms or 2.78 x 10²³ atoms.
Caution => When to use H vs H₂ => This problem is specific for 'hydrogen atoms' but some may simply say hydrogen. In such cases use H₂ or 'molecular hydrogen' is the focus. it's a matter of semantics, H vs H₂.
Answer: 1.284M NH3
Explanation: (12.23 grams)/(17.0 gramms/mole) = 0.7191 moles
Dissolved in 560.0 ml (=0.5600L)
(0.7191 moles)/(0.560L) = 1.284M (4 sig figs)