Not a homework or exam or anything - just one of a list of a few scenarios that we can try on our own - but he has no 'answer key.'
Still sounds like school work. You won't learn anything if we do you school work for you.
There are several parts to the assignment.
Write software to print square root of first 100 natural numbers on the serial console
You need to be able to print to the serial console. You need to be able to compute the square root of a value. You need to understand int vs. float, and choose the appropriate storage type. You need to determine how to perform an action a specific number of times. You need to decide whether a value is a natural number or not (whatever that means).
You will learn nothing if we do any of this for you.
If you try something, and it does not work, and you explain what you expected and what you got, we'll be happy to point out what is wrong, and suggest how you might fix it.