Someone !

what must be true for any endothermic reaction?

the chemical bonds of the products have more energy than the chemical bonds of the reactants.

there are more products than there are reactants.

there must be a phase change from solid to liquid or from liquid to gas.

the reaction must take place in a sealed container held at constant volume.

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6