Who is the richest person in the United States of America? (Used 'richest' as it's a one-syllable adjective to form the superlative).
What is the longest river in Russia? (Used 'longest' as it's a one-syllable adjective to form the superlative).
Where is the oldest theatre in Europe? (Used 'oldest' as it's a one-syllable adjective to form the superlative).
What is the most beautiful building in Moscow? (Used 'most beautiful' because 'beautiful' is a multi-syllable adjective and requires 'most' for the superlative).
Who is the youngest in your class? (Used 'youngest' as it's a one-syllable adjective to form the superlative).
Who is the most popular actor in Britain? (Used 'most popular' because 'popular' is a multi-syllable adjective and requires 'most' for the superlative).
Who is the most intelligent pupil in your group? (Used 'most intelligent' because 'intelligent' is a multi-syllable adjective and requires 'most' for the superlative).
Where is the hottest climate in the world? (Used 'hottest' as it's a one-syllable adjective ending in a consonant preceded by a vowel, so we double the consonant and add -est for the superlative).