Eight of us go fourth, not back, to protect our king from an attack. What are we?

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

Move three sticks of the spiral below to form a square.

You have two buckets - one holds exactly 5 gallons and the other 3 gallons. How can you measure 4 gallons of water into the 5 gallon bucket?

(Assume you have an unlimited supply of water and that there are no measurement markings of any kind on the buckets.)

Forwards I am heavy, backward I am not. What am I?

Spelt forwards I’m what you do every day, spelled backwards I’m something you hate. What am I?

Your mother’s brother’s only brother-in-law is asleep on your couch. Who is asleep on your couch?

You see a boat filled with people, yet there isn’t a single person on board. How is that possible?

There are five vowels (a, e, i, o, u) in the English language.
Can you tell us a word that contains all these vowels?

In my garden, I have many trees but only one of them is the mango tree. In these mango trees, there are some mangoes(as expected).

But after a strong wind, there are neither mangoes on the tree nor on the ground. Explain?