அவர் பரிசு வெல்வார் என்று நான் உறுதியாக நம்புகிறேன்.

இதை எப்படி இங்கிலீஷ்ல சொல்லுவீங்க?

Answer
I am sure he will win the prize. [or]
I bet he’ll win the prize,

Note:

1. “I bet/I’ll bet (that)” is a way to say that you know something for sure.
   Eg: I bet Ravi has taken the book.
2. It is used to show that you understand what someone just said or that you agree with them.
   Eg: “I couldn’t refuse such a good offer.” – ‘I’ll bet!’