In the reaction 
 
the electrophile involved is

1. Dichloromethyl cation $\left(\stackrel{\oplus }{\mathrm{C}}{\mathrm{HCl}}_2\right)$

2. Formyl cation $\left(\stackrel{\oplus }{\mathrm{C}}\mathrm{HO}\right)$

3. Dichloromethyl anion $\left(\stackrel{\oplus }{\mathrm{C}}{\mathrm{HCl}}_2\right)$

4. Dichlorocarbene (:CCl₂)

Which one is the most acidic compound ?

The most acidic compound among the following is:

1.		2.
3.		4.