What is so fragile that saying its name breaks it?

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 ?

Can you write down eight eights so that they add up to one thousand?

Is the statement valid that it does not matter how much older a sibling is, eventually the younger one will be half as old as the older one?

Can you count the number of triangles in the given picture?

4 fathers, 2 grand-fathers and 4 sons went to watch the movie.What is the minimum number of tickets they need to buy ?

If you say my name, I will no longer exist. What am I?

I am white when I am dirty, and black when I am clean. What am I?

Two prisoners Jack and Jill are locked in a cell.
There is open window approx 40 feet above the ground of the cell.
They are never able to reach there.

Then they plan to escape by a tunnel and they start digging out.
After digging for more than 20 days, Jill comes with the different plan and they escaped.

what was the plan ?

You throw me out when you want to use me and you take me in when you don't want to use me.

Who Am I?