Question 777704
Square root of 7 is exactly one number.  Yes, it is irrational.  To say that it is an ELEMENT of the irrationals makes more sense than to say it is a subset of them.  IF YOU HAVE a rule that describes a set of numbers and square root of 7 be the only number which fits the rule, then you may be able to say that square root of 7 be a subset of the irrational numbers.  Having not been given such a rule, square root of 7 is an element of the set of irrationals.