What significant action did Khrushchev take in 1956?

The correct answer is Option 3 - He introduced some reforms and denounced Stalin's leadership style.

In 1956, Khrushchev introduced some reforms and denounced Stalin's leadership style, marking a significant shift in Soviet policies.
Nikita Khrushchev, born in 1894 and leading the Soviet Union from 1953 to 1964, is known for his denunciation of Stalin's leadership style and the introduction of certain reforms in 1956. He advocated the idea of "peaceful coexistence" with the Western powers and played key roles in suppressing a popular rebellion in Hungary and the Cuban missile crisis.