What is an example of a dilute solution that you can find at home? what would be the specific use of that diluted solution?

Can someone me with these questions plz.

Which atom or ion is the largest? a. k b. k+ c. ca d. ca2+ e. li

Which statement is true about this reaction? 14n+1h 15o it is a practical source of energy on earth. it occurs only outside the solar system. its product is heavier than each of its reactants. it shows the critical mass of an element.