Explanation:

Both statements are correct.

• The boundary between present-day Assam and Mizoram, 165 km long today, dates back to the colonial era, when Mizoram was known as Lushai Hills, a district of Assam.
• Mizoram was part of Assam till 1972.
• In 1972, it became a separate Union Territory.
• In 1987, it became a full-fledged state.
• The three South Assam districts of Cachar, Hailakandi and Karimganj share a 164.6 kilometre-long border with Mizoram’s Kolasib, Mamit and Aizawl districts.
• Mizoram borders Assam’s Barak Valley. Both the states border Bangladesh.

Hence option 4th is correct.