What are the similarities between potassium nitrate and potassium chloride?

Both contain ;-

potassium cations (K^(+))

acid anions (NO3^(-) & Cl^(-)).

can be made from potassium hydroxide and the corresponding acid.

soluble in water as the solvent.

high melting point

electrical conductor when in solution

crystalline solid; does not conduct electricity when solid.

when solid they are both white in colour

non-poisonous (but ingestion is NOT recommended).

flame test is 'lilac'(pale purple) in colour due to potassium cations.

One difference ;-

Using Barium nitrate test.

KNO3 does NOT produce a precipitate. (common nitrate ion)

KCl produces a WHITE precipitate of barium chloride. (classic halogen test).