Mongolia is 11 times larger than Tajikistan.
Area: 1,564,116 km2 World Factbook
Population: 2,953,190 (July 2014) World Factbook
Mongolia is a landlocked country in east-central Asia. It is bordered by Russia to the north and China to the south, east and west. Ulaanbaatar, the capital and also the largest city, is home to about 45% of the population. Mongolia's political system is a parliamentary republic. Wikipedia
Area: 143,100 km2 World Factbook
Population: 8,051,512 (July 2014) World Factbook
Tajikistan, officially the Republic of Tajikistan, is a mountainous landlocked country in Central Asia. It is bordered by Afghanistan to the south, Uzbekistan to the west, Kyrgyzstan to the north, and China to the east. Mountains cover more than 90% of the country. Wikipedia