Final answer:
Mikhail Gorbachev was the 20th century Soviet leader whose reforms led to the collapse of the Soviet Union in 1991.
Step-by-step explanation:
The 20th century Soviet leader whose reforms led to the collapse of the regime was Mikhail Gorbachev. He assumed power in 1985 at a time when the Soviet Union was facing significant economic issues and a costly war in Afghanistan. Gorbachev introduced substantial reforms such as glasnost (openness) and perestroika (restructuring), which aimed to modernize the economy and open up the Soviet society. These reforms, however, accelerated the demand for independence within various Soviet republics and ultimately facilitated the dissolution of the Soviet Union in 1991. Thus, the correct answer to the student's question is 3) Mikhail Gorbachev.
The 20th century Soviet leader whose reforms led to the collapse of the regime was Mikhail Gorbachev. Gorbachev became the leader of the Soviet Union in the mid-1980s and initiated a dramatic restructuring of Soviet political and economic policies. His reforms, known as perestroika and glasnost, aimed to modernize the Soviet economy and bring more openness and transparency to the government. However, these reforms ultimately led to the dissolution of the Soviet Union and the end of the Cold War.