So In this example question it says which of the following choices represents A monoatomic element that is also a chalkagen. Remember some groups have unique names. Achalcogen is from group 6A or what we know as group 16. So if we come up here, groups 6A or group 16, which is the same thing, would be this column.
Here oxygen, sulfur and selenium are automatically out because none of them are monoatomic. The monoatomic elements from this group would be Te, Po or Lv. If we look, A couldn't be our answer because it's monoatomic, but it is not a chalka jet. Sulfur is a chalcogen because it's in that group 6A, but it is polyatomic. Te is one of the three that we name.
So what's our answer? Chlorine is not a chalk Cogen. It's in Group 7/8, so it's a halogen. Also it's diatomic. Then finally, lithium. Lithium is monoatomic, yes, but it is an alkali metal and not a chalk gene. It's in Group 1A. So out of all our choices, only option C is the correct answer here.