Which electrolyte is used in an alkali fuel cell? a high-temperature carbonate salt mixture a solid polymer a solid ceramic metal oxide compound an aqueous potassium hydroxide solution

  an aqueous potassium hydroxide solution

An alkaline fuel cell is a zero-emission device whose one major component is the electrolyte. An electrolyte, on the other hand,  is a solution that is able to conduct electricity. In an alkaline fuel cell. The electrolyte is an alkaline liquid, and potassium hydroxide also known as KOH is the only alkaline liquid among the choices. 

Explanation:

edg 2021

1. they vary with a higher number because boiling is way hotter than melting