I noticed that there are time period in which Forex pairs most active than others. Why is that so? For eg. When (GMT) is EUR/USD very active?
Because of trading sessions.
or you can watch this video for more explanation for example -
A Breakdown of the Forex Trading Day
Unlike the futures and equities markets, the forex market trades actively 24 hours a day with active trading hours following the sun around the globe to each of the major money centers.As the foreign exchange market is an over the counter market where two counterparties can trade with each other whenever they want, technically the market never closes. Most electronic trading platforms however open for trading at around 5 PM Eastern Time on Sunday, which corresponds to the start of Monday's business hours in Australia and New Zealand. While there are certainly banks in these countries which actively make markets in foreign exchange, there is very little trading done in these countries when compared to other major money centers of the world.The first major money center to open and there fore the start of the first major session in the forex market is the Asian Trading session which corresponds with the start of business hours in Tokyo at 7pm Eastern Time on Sunday.While still considered 1 of the three major money centers, only 7.6% of forex transactions flow through Tokyo trading desks, so the Asian trading session is the least active of the three. While there is active trading in Yen based currency pairs during Asian hours the market for currencies outside of Yen based pairs is relatively thin, making Asian trading hours a time when the larger banks and hedge funds in the market will sometimes try and push the market in their favor.Next in line is the European trading session which begins with the start of London business hours at 2 AM Eastern Standard Time. While New York is considered by most to be the largest financial center in the world, London is still king of the forex market with over 32% of all forex transactions taking place in the city. Before the Euro there were more than a dozen additional currencies in Europe making foreign exchange part of every day life for both individuals and businesses operating in the region. In addition to this, London is situated perfectly from a time zone standpoint with business hours for both the large eastern and western economies taking place during London trading hours.As London is the most active session in the forex market it is also the session with the most volatility for all the currency pairs which we will be studying in this course.Last but not least is the US session which begins with the start of New York business hours at 8 AM Eastern Standard Time. New York is a distant second to London in terms of forex trading volumes with approximately 19% of all forex transactions flowing through New York Dealing Rooms.The most active part of the US Trading session, and the most active time for the forex market in general, is from about 8am to 12pm when both London and New York trading desks are open for business. You can see very large volatility during this time as in addition to both New York and London trading desks being open, most of the major US economic announcements are released during these hours as well.
The trading day winds down after 12pm New York time with most electronic platforms closing for business at around 4 PM Eastern Standard Time on Friday.