Egg white, turns violet when two drops of copper sulphate and ten drops of caustic soda is added to it. This indicates the presence of 

When two drops of copper sulphate and ten drops of caustic soda or NaOH is added to egg, it turns violet. This indicates the presence of proteins.
This is Biuret's test and the principle is simple as follows:
In the presence of alkaline medium (caustic soda or NaOH), the $C{u}^{2+}$ ions get reduced to $C{u}^{+}$ and binds to the egg proteins, thereby giving a violet color.
Therefore, the correct answer is option B.