I think it is b..................................................
Put the <em>wood and excess oxygen in a closed contai</em>ner that contains some device that can create a spark (to start the reaction).
Determine the <em>mass of container + contents</em>.
<em>Start the reaction</em> and, after everything has cooled down, again determine the <em>mass of container + contents</em>.
If the two masses are the same, you have demonstrated that the reaction obeys the Law of Conservation of Mass.
1 mol ------------ 6,02×10²³
0,17 mol ------- X
X =(0,17×6,02×10²³)/1
X = 1,0234×10²³ molecules H₂O
:•)