Final answer:
The number is -13.
Step-by-step explanation:
To determine the number that is a real number, a rational number, not a natural number, and less than -13, we can eliminate options b) -14 and d) -15 since they are not rational numbers. A rational number is a number that can be expressed as a fraction, and both -14 and -15 cannot be expressed as fractions. We are left with options a) -12 and c) -13. Since -12 is greater than -13, the number must be c) -13.