How many letters does the top answer for “alan reed is known for providing the voice of which character” have?

The most common answer is flintstone (10 letters).

Crossword clue: alan reed is known for providing the voice of which character

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

flintstone 10 letters otdb

fred 4 letters otdb

a radioactive element of the alkali-metal group discovered as a disintegration product of actinium