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Can I say,

(a) She cooked many food. They were delicious. They enjoyed on Deepavali Day.
(b) She cooked some food and dishes.
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"food" is a non-count noun. You can only use "many" with a count noun.

She cooked a lot of food. It (food is singular, no matter how much food there was) was delicious. They enjoyed (no preposition here) Deepavali Day.
Comments  
Can I say,

(a) She cooked many food. They were delicious. They enjoyed on Deepavali Day.
(b) She cooked some food and dishes.
 AlpheccaStars's reply was promoted to an answer.