Arrange the following events related to disintegration of the Soviet Union in chronological order:

(A) Boris Yeltsin is appointed as the head of the Communist Party in Moscow.

(B) Soviet Union declares that the Warsaw Pact members are free to decide their own future.

(C) Boris Yeltsin becomes the President of Russia.

(D) The Commonwealth of Independent States is established.

The correct option is (A), (B), (C), (D).

To arrange these historic events related to the disintegration of the Soviet Union in chronological order, let us look at the timeline of each event:

(A) Boris Yeltsin is appointed as the head of the Communist Party in Moscow:
In December 1985, Mikhail Gorbachev appointed Boris Yeltsin as the First Secretary of the Moscow City Committee of the Communist Party of the Soviet Union, introducing him to the high-ranking leadership of the USSR.

(B) Soviet Union declares that the Warsaw Pact members are free to decide their own future:
In October 1989, the Soviet Union under Gorbachev officially abandoned the Brezhnev Doctrine, declaring that the member states of the Warsaw Pact were free to decide their own destiny. This policy was famously dubbed the "Sinatra Doctrine."

(C) Boris Yeltsin becomes the President of Russia:
In June 1991, Boris Yeltsin was elected as the President of the Russian Soviet Federative Socialist Republic (RSFSR) in the first democratic presidential election in Russia's history.

(D) The Commonwealth of Independent States is established:
On December 8, 1991, the leaders of Russia, Belarus, and Ukraine signed the Belavezha Accords, declaring the dissolution of the Soviet Union and establishing the Commonwealth of Independent States (CIS) to coordinate relations among the newly independent post-Soviet republics.

By ordering these events chronologically from earliest to latest, we get:
(A) December 1985 → (B) October 1989 → (C) June 1991 → (D) December 1991.
Thus, the correct sequence is (A), (B), (C), (D).