Answer :

To determine which radioisotope is a beta particle emitter, we need to consider the emission types of each given radioisotope. Let’s look at the emission types:

- 90Sr (Strontium-90): This isotope is known to emit beta particles.
- 220Fr (Francium-220): This isotope emits alpha particles.
- 37K (Potassium-37): This isotope emits beta particles.
- 238U (Uranium-238): This isotope emits alpha particles.

Among the options provided:

A) 90Sr is a beta particle emitter.
B) 220Fr is an alpha particle emitter.
C) 37K is a beta particle emitter.
D) 238U is an alpha particle emitter.

Among the given choices, we need to identify a beta particle emitter. We can see that there are two beta particle emitters listed: 90Sr and 37K. Given the provided options, the correct answer is:

A) 90Sr

Therefore, the correct answer is 90Sr.