Solution:

Pizza

Explanation:
Pizza is served to people with 2 E's and rest are served Burgers.

Solution:

1

Explanation:
Because I have only one mouse and not a pair required for reproduction.

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:

Fishing Net

Solution:

A Party

Solution:

The poison was not in pills but in water.

Solution:

It can be done as shown below.

Solution:

12

Solution:

RS

Explanation:
The list is formed by using last two letter of planet's names in the order from Neptune To Mercury

NEPTU-NE
URAN-US
SATU-RN
JUPIT-ER
MA-RS
EAR-TH
VEN-US
MERCU-RY

Solution:

A thermometer