Solution:

The prisoner picks a marble and without showing it to anyone swallows it and then picks the remaining marble and shows to everyone which was black which proved the first marble prisoner pick must be white.
The Mad King has no option but to let the prisoner go.

Solution:

6

Explanation:
Key1: 3 attempts for 3 gates.
Key2: 2 attempts for remaining 2 gates.
Key3: 1 attempts for the last gate.

Solution:

11

Explanation:
Tzu‑ying won 3 games
V.Sindhu must win 3(to balance 3 games she lost) + 5 games(required for min 50$) = 8 games
Total Games = 3 + 8 = 11 games.

Solution:

The poison was not in pills but in water.

Solution:

When blind man "Grandpa" opened his bandages, the train must be passing through the dark tunnel. The man thought he was still blind and hence commit suicide.

Solution:

On phone, using pause button, the teller messaged to her mother "Emergency mother, call help".

Explanation:
all Except one in bold is paused by the teller.
Is there an emergency mother, Call me when you reach home and I will help you with the dinner.

Solution:

Cup-8

Explanation:
This might be tricky for mobile users where the bottom cup is difficult to focus on.

Solution:

47.

Explanation:
Aarav is 6 years old and his sister Arshika is half of his age, which indicates Arshika age is 3 years less than Aarav's age. So when Aarav is 50, Arshika will be 47

Solution:

East

Explanation:
- Right Turn => North Direction
- About Turn => south Direction
- Left Turn => East Direction

Solution:

The man with the cast

Explanation:
Reason-1: The blood strain is on the left side of the dead man which means the killer is most likely a left-handed. The cashier and man with the cashier are both right-handed.

Reason-2: Why will a man with the cast go for buying shirts/coat? Seems suspicious.

Reason-3: The man with the cast must be carrying the weapon inside the cast.