What's the only room from which no one can enter or leave

My cousin lives in one story house in Antarctica. His house is made the of-of sandstone. what is the color of stairs?

Can you place six X (crosses) in below board without making three in a row in any way ?

John and Jill are madly in love with each other. To remind Jill of his pure love, John wants to send her a ring by post but in their country where burglary is quite prominent, any package that is not locked comes under the risk of being stolen for the contents.

John and Jill possess many padlocks but neither one of them has the other key.

Can you find a way John can send the ring to Jill safely?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

There is a box. The area of its top is 240 square units, the area of the front is 300 square units and the area of the end is 180 square units.

Can you calculate the dimensions of this box with the given data?

In the image below, you can see two glasses and two matchsticks.You need to move four matchsticks in such a manner that the crosses come inside the glasses. Note: you cannot move the crossed.

You know three triplets: Frank John and Wayne (need to return your money). Frank always tells the truth while John and Wayne always lie. You meet one of them on the road and can ask him a three-word question.
Which question, will you ask?

Which five letter word can be added at the end of below word to form a
valid word?

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