"Ela vai ser a responsável pela área de comunicação."

Translation: She will be responsible for the communication area.

[G.P.Niers]

Why is there ‘a’ in this sentence?

[mkorn5]

I´ve occasionally heard responsible used as a noun in American English, meaning responsible party or responsible officer. In the context of this sentence, "She will be the responsible (officer) for communications."

However this usage is uncommon, and a quick google search didn´t yield any dictionary references that would support it being technically correct.

[G.P.Niers]

Ah, so ‘a responsável’ is ‘the one responsible’. That makes sense.

But when you're e.g. dividing tasks you'd leave out ‘the one’ and simply say ‘She'll be responsible for ...’.

Still, I just did some web searching and even in Portuguese it seems to be more common to leave out ‘a’.

[Paulenrique]

Yes. A/o responsável = the one responsible. Just responsável means "be in charge of". As in English, resonsável is also an adjective, both for male and female and its plural is "responsáveis"