Emulsifiers?

=From the article "//Emulsifier Applications//"=

Q & A section:
An emulsifier has a hydrophilic part (water-loving) and lipophilic part (oil-loving) at the same time in its chemical structure. This enables the emulsifier to bind water and oil in foods together.
 * 1. What is the unique characteristic that contributes to the excellent functionality of an emulsifier?**

i) Ionic charge ii) Crystal stability iii) HLB
 * 2. State 3 criteria that are used in selecting a suitable emulsifier.**