If a person’s phenotype is that they cannot roll their tongue, what is their only possible genotype?

Uhh I'm really not sure if not rolling the tongue is dominant or recessive, but judging by the fact that you said their "only possible" genotype, I'm assuming it's homozygous recessive

what image you forgot to include it.

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds