Elsa is making a grilled ham-and-cheese sandwich. She uses a 20-gram slice of cheese, 40 grams of sliced ham, and two 15-gram slices of bread. After she heats the sandwich on a griddle, the cheese is melted. What will be the mass of her sandwich?

90 grams. When the state of an object changes, the mass doesn’t change.

*edited*

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