Forex transaction-which rate to apply ?/

Practically, companies take monthly average rates to account foreign transactions, But in case, you are using spot rate(i.e. date of transaction), then you may refer RBI rates at the following link:

https://www.rbi.org.in/scriptts/ReferenceRateArchive.aspx

Accounting entry will be as follows:

1) Purchase A/c Dr.              2500 X 54.47

                To Vendor A/c                         2500 X 54.47

2) Vendor A/c Dr.                     2500 X 55.83

                To Bank A/c                             2500 X 55.83

3) Exchange Fluctuation A/c Dr.      2500 X(55.83-54.47) 

                To Vendor A/c                            2500 X(55.83-54.47) 

Alternatively Bank TT rates(both-buying & selling rates) can also be considered