Final answer:
The largest religious group in Russia and the Western Republics is the Russian Orthodox Church, although only 15-20% actively practice it. Islam is significant in the region as well, particularly in the Caucasus and southern Urals.
Step-by-step explanation:
The largest religious group in Russia and the Western Republics is the Russian Orthodox Church. Historically, it was the official church of Russia, with a large portion of Russian citizens traditionally considered Orthodox Christians. However, during the Soviet era, the church faced significant persecution. As a result, contemporary practice of Orthodoxy has reduced to about 15 to 20 percent of the population, although a larger number identify as Russian Orthodox. Another substantial religious group in this region practices Islam, particularly in the Caucasus region and the southern Ural Mountains, accounting for roughly 15 percent of the population. Other Christian denominations and religions such as Buddhism and indigenous Siberian tribal religions also have a presence, albeit smaller.