Which of the following is a Lewis base?

$Cl^-$ is the conjugate base of .....

$NaOH$ is a strong base because

The dissociation of $H_3PO_4$ takes place in how many steps?

Observe the following species: $AlCl_3, NH_3, H^{+}, Co^{3+}, OH^{-}, H^{-}, Mg^{2+}, BF_3, Cl^{-}$. How many Lewis bases are present in the above list?

An amphoteric anion is capable of both accepting and donating a proton in a suitable medium. Which of the following ions exhibits this property?