"These fruits are cold."
Translation:ये फल ठंडे हैं।
ठंड means cold as a general noun, more like "coldness", whereas ठंडा ठंडे and ठंडी are more like adjectives. Which to use just depends on whether the person you are talking about is male, female, or multiple people. Since फल is being used plurally in this sentence, ठंडे