The correct statement about the S_N1 reaction is:

Which one of the following statements is not correct for a nucleophile?

1. Nucleophile is a lewis acid.
2. Ammonia is a nucleophile.
3. Nucleophiles attack low electron density sites.
4. Nucleophiles are not electron-seeking.

The species among the following that is not an electrophile is:

1. $B{H}_3$

2. $H_3\stackrel{\oplus }{O}$

3. $\stackrel{\oplus }{N}{O}_2$

4. $\stackrel{\oplus }{Cl}$