An irrational number is a number in which its decimal numbers are infinite and without periodicity. In the given numbers you have:
-7/4 = 1.75 no irrational
2/3 = 0.6666... this is a periodic decimal number, so,it is not irrational
√3 = 1.7320508.. number with infinite decimals without periodicity, then, it is irrational.
√4 = 2 interger number, no irrational
