Final answer:
The capital of the country represented by number 5 on the map, which is landlocked and borders countries 4 and 3, is La Paz, which is one of the capitals of Bolivia.
Step-by-step explanation:
The capital of the country represented by number 5 on a political map of South America, which is landlocked and shares borders with the countries labeled number 4 and number 3, along with a smaller number 8, is La Paz. This corresponds to the country of Bolivia, which is indeed landlocked, lying to the south of Peru (number 4) and to the west of Brazil (number 1). It borders Chile (number 3) to the southwest and shares a smaller border with Argentina (number 8). Bolivia has two capitals: La Paz, where the government is seated, and Sucre, the constitutional capital. The presence of the Andes Mountains and the diverse climate due to variations in altitude are important physical characteristics of Bolivia.