Webb has calculated the percent composition of a compound. how can he check his result?
by making sure they are in the lowest ratio
by adding them to see if they total 100
by checking that they are whole-number multiples
by dividing them by the molar mass

second choice, by adding them to see if they total 100.

Explanation:

Percent composition of a compound tells the amount of each element taken 100 as a base of total amount, hence it adds up 100.

You can check it mathematically in this way.

Assume you have an amount n of a compound formed by many elements, and that the amounts of each element are n₁, n₂, n₃ ,, were n₁ + n₂ + n₃ + ... = n.

When you find the percent of each element you find:

%n₁ = n₁ / n × 100

%n₂ = n₂ / n × 100

%n₃ = n₃ / n × 100 and so on.

Now, when you add all the percents you get:

n₁ / n × 100 + n₂ / n × 100 + n₃ / n × 100 + ... = [n₁ + n₂ + n₃ + ... ] / n × 100 =

= n/n × 100 = 1 × 100 = 100.

Therefore, the sum is 100, and this is a way to check your result.