esta instead of estas

Question

Why is this the correct answer: Usted esta en la lista and not Usted estas en la lista?

Answer

Usted is formal singular while Ustedes is plural. We'd say "Ustedes están en la lista" if we were referring to a group of people, where in this example it seems we're only referring one person.

Answer

Hola Roger,
yes, as R'Shaun was saying, in other words, usted is a formal you, (formal tú) but we conjugate the verb as if it was él/ella (not tú), so, with estar, it goes:

yo estoy
tú estás
él/ella/usted está
nosotros estamos
vosotros estáis
ellos/ustedes están

I hope this helps.
Inma