Which of the following species can act both as an acid as well as a base ?

Which can act as an acid as well as a base-

Any species capable of accepting a lone pair of electrons acts as a lewis acid, where as a species capable of donating a proton acts as a Bronstead acid. Which of the following can act as a lewis acid as well as a lewis base ?

Any species capable of accepting a lone pair of electrons acts as a lewis acid, where as a species capable of donating a proton acts as a Bronstead acid. Which of the following can act as a lewis acid as well as a lewis base ?

Which of the following can acct both as a Bronsted acid as well as a Bronsted base ?

Which of the following species can function both as oxidizing as well as reducing agent ?

Which of the following species can function both as oxidizing as well as reducing agent?

Which of the following species can function both as oxidizing as well as reducing agent?

Which of the following species can acts as bronsted base as well as a Lewis base?