We are having transactions in accouts receivable, we have collections in dollar, and we are using peso in our books. At the end of the month, all transactions in dollar, will be used in the average rate. Thus, we have to compute the realized/unrealized gain/loss.
I want to be very sure if what entry to used,is it realized / unrealized?

Not quite sure about what acounts you used. However my client used to use one separate account to post Fx transactions. Lets take AR Fx /AC,say home currency is USD and transaction happened in EUR.Then to convert amounts.. entry would be..

AR Original A/C (Home Currency) Dr. USD XXX
Fx Gain and Loss A/C Cr. USD xxx
Fx Gain and Loss A/C Dr EUR XXX
AR Fx A/C Cr EUR XXX