Among the following examples, the species that behave(s) as a Lewis acid is/are: 
$B{F}_3,SnC{l}_2,SnC{l}_4$ 
1. Stannous chloride, stannic chloride
2. $B{F}_3$, stannous chloride
3. Only $B{F}_3$
4. $B{F}_3$, stannous chloride , stannic chloride

Conjugate acid of NH₂^– is:

1. NH₄OH

2. NH₄⁺

3. \(NH_{2}^{-}\)

4. NH₃

A compound among the following that cannot be classified as a protonic acid is: