Solution:

Typewriter

Solution:

I Am stone.

Explanation:
Stone is 5 letter word. if remove word one(not 1 letter) we will get st.

Solution:

The letter 'n'.

wiNdow - widow
door - doNor

Solution:

Heroine

Solution:

Unquestionably

Solution:

I am DAVID.

At the core I have 5
If we talk in roman numeric system, 5 = V

Similarly, 500 stands in the beginning and end
500 = D

I also include the first letter i.e. A and the first number i.e. I (in roman numeric system)

All of them combine to form DAVID.

Solution:

Mississippi.

(For example, One Mississippi, Two Mississippi, and Three Mississippi etc.)

Solution:

Paradise

Solution:

The word is Energy.
Nobody said anything about the order of 'g', 'r' and 'y' at the end of the word.
Also, we use energy every day.

Solution:

I am ERROR