17. When 1 mol of the following substances react completely with oxygen, the

substance that consumes the least oxygen is

A. Na

B. Ca

C. AI

D. H2

Option A. Na

Explanation:

Let us generate a balanced equation for the reaction of O2 with the individual elements. This is illustrated below:

1. 4Na + O2 - > 2Na2O

From the equation,

4moles of Na comsumed 1mole of O2.

Therefore, 1mole of Na will comsume = 1/4 = 0.25mol of O2.

2. 2Ca + O2 - > 2CaO

From the equation,

2moles of Ca consumed 1 mole of O2.

Therefore, 1mole of Ca will consume = 1/2 = 0.5mole of O2

3. 4Al + 3O2 - > 2Al2O3

From the equation,

4moles of Al consumed 3moles of O2.

Therefore, 1mole of Al will consume = 3/4 = 0.75mol of O2

4. 2H2 + O2 - > 2H2O

From the equation,

2moles of H2 consumed 1mole of O2.

Therefore, 1mole of H2 will consume = 1/2 = 0.5mole of O2

The following data were obtained from the above calculations:

1mole of Na requires 0.25mol of O2

1mole of Ca requires 0.5mole of O2

1mole of Al requires 0.75mol of O2

1mole of H2 requires 0.5mole of O2

From the above, we see clearly that 1mole of Na consumes the least amount of O2

I would say Na. Oxygen has 2 valence electrons and when reacting with other molecules, the ones with the fullest or emptiest shells will react the least. Both H2 and Na are in the Alkali Metals in the first row, but since H2 has 2 molecules, it would use more oxygen than Ana