The correct answer is (b) a day dreamer.
Idiom: 'Head in the clouds' — describes a person who is out of touch with reality, living in fantasies, or indulging in impractical or unrealistic thoughts and dreams.
Example: 'He always has his head in the clouds — he never thinks practically.'
Bangla: যে ব্যক্তি বাস্তবতা থেকে বিচ্ছিন্ন, দিবাস্বপ্নে বিভোর।
✗ 'proud' — unrelated; pride is expressed through different idioms (e.g., 'high and mighty').
✗ 'an aviator' — a pilot; the idiom has nothing to do with flying.
✗ 'a philanthropist' — a person who helps others through charity.
Source: Cambridge Idioms Dictionary; Longman Dictionary of English Idioms.