Verified Answer :

The denominator is always the number under so in this fraction, we can say 23 is the denominator because it is the number under

When number is in fraction form, like p / q, then bottom number is known as denominator and upper number as numerator. 
Here, upper number (numerator) = 1
& lower number (denominator) = 23

In short, Your Answer would be 23

Hope this helps!