Is 7.5 a rational, irrational, natural, whole, integer or real number?
Any number that can be written as a fraction, or in other words the ratio between two numbers, is a rational number.
It is also a real number as rational numbers are a sub-set of the collection of real numbers.
Let's do all the definitions:
Natural : counting numbers: 1, 2, 3, 4, 5...
Whole and integer : as before, but including the zero and negative numbers: ..... -3, -2, -1, 0, 1, 2, 3,...
Rational : all numbers that can be written as a ratio = a fraction
... -3/1 -2/3 -257/347 0 14/3 22/7....
Irratonal : all numbers that can not be written as a ratio: the square root of 2, pi, e, ....
Real numbers : all of the above put together. You can use real numbers to measure real things, like length or temperature.
There is a set of numbers outside this realm, and they're called imaginary and complex numbers, and they all are connected to the square root of -1.