If the digits of a number add up to 9, what number is it divisible by?

It's divisible by 9

Step-by-step explanation:

9 and also 3

Step-by-step explanation:

Numbers whose digits add up to 9 are divisible by 9. For example 18, 27, 36, 45, 54, 63, 72, 81 are all divisible by 9.

Numbers whose digits add up to any number divisible by three are divisible by three. So 237 has a digit sum of 2+3+7= 12. 12 is divisible by three, so 237 is divisible by three.

In this question any number with a digit sum of 9 is divisible by three as well as 9.

You have described a scenario where nitrogen is the limiting reagent since:

2 N2 + 6 H2 → 4 NH3

You could make four molecules of ammonia and have four molecules of hydrogen left over.