Use 'quel' before masculine singular nouns starting with a regular consonant (like 'il'). Use 'quello' before nouns starting with z, s+consonant, gn, ps, or x (like 'lo').
Quello — 'Quel' (Masculine Singular, Regular Consonant)1 / 10
___ psicologo (that psychologist, m.sg — starts with ps)