Question

Given the reaction: 2na + 2h2o → 2na+ + 2oh− + h2

Answer 1

Answer:

$\large \boxed{\text{3. Na}}$

Explanation:

We can use oxidation numbers to decide which substance is reduced.  

$\rm 2\stackrel{\hbox{0}}{\hbox{Na}} + 2\stackrel{\hbox{+1}}{\hbox{ H}_{2}}\stackrel{\hbox{-2}}{\hbox{O}}\longrightarrow \rm 2\stackrel{\hbox{+1}}{\hbox{Na}^{+}} + 2\stackrel{\hbox{-2}}{\hbox{O}}\stackrel{\hbox{+1}}{\hbox{H}^{-}} + \stackrel{\hbox{0}}{\hbox{H}_{2}}$

The oxidation number of Na changes from 0 in Na to +1 in Na⁺.

The oxidation number of H changes from +1 in H₂O to 0 in H₂.

$\text{An increase in oxidation number is oxidation, so \large \boxed{\textbf{Na}} is the substance oxidized.}$

1 and 4 are wrong because H₂ and Na⁺ are products.

2. is wrong because there is no H⁺ to be oxidized or reduced.