What is more useful when it is broken?

Can you name an animal whose killing cannot be performed without spilling your own blood?

Can you find out the remainder when 3^300 is divided by 5?

If you drop me I’m sure to crack, but give me a smile and I’ll always smile back. What am I?

What work can one never finish?

I am a type of food that is often found in the fridge and can be white in colour. What I am?
Hint 1: I am a dairy product.
Hint 2: You can spread me on the bread.

What breaks yet never falls, and what falls yet never breaks?

An office is divided into 8 cubicles. How many of the cubicles are painted if only 1/8 of the cubicles are painted?

By including only four matchsticks in below picture, you have to make "Four Triangles And Two Squares"

John is found dead in his office at his desk. The police have narrowed the suspects down to three people: Mrs. Jacob, John’s wife Hena and his business partner Jason . All three visited John on the day of his murder, but all three provide the police with stories of explanation as to the reason for their visit.
Police found John with his wrist watch still on his right arm, a torn up picture of his wife laying on the floor beside the trash can, and an ink pen in his right hand. On the desk, the police found a name plate, a telephone that was off the hook, and a personal calendar turned to the July 5th page with 7B91011 written on it. After examining this evidence, the police knew their suspect. Who was it ?