Answer:

Explanation:
We will need a balanced chemical equation with masses, moles, and molar masses.
1. Gather all the information in one place:
Mᵣ: 18.02
2Na + H₂O ⟶ 2NaOH + H₂
m/g: 72.0
2. Moles of H₂O

3. Moles of Na
The molar ratio is 2 mol Na/1 mol H₂O.

Carbon is the answer. all hydrocarbures have to contain carbon.
You have to move the decimal point forward 2 times to make the number 3.4,which makes the scientific notation 3.4×10^-2