What you cannot hold but it is yours?

You can hear me, but you can't touch or see me.

What am I?

Can you tell a 3D object that has just two surfaces?

Can you place three balls such that the equation shown in the picture holds true?

A four-digit number (not beginning with 0) can be represented by ABCD. There is one number such that ABCD=A^B*C^D, where A^B means A raised to the B power. Can you find it?

I had an infinite supply of water and 5 litres and 3 litres jars.

How would you measure exactly 4 litres in the least number of steps?

How many triangles are there in the picture below?

Can you find out the missing number?

? 4 5 3 5

9 5 7 10 3

John is looking at Jenifer, but Jenifer is looking at Jacob. John is married, but Jacob is not.

Is a married person looking at an unmarried person ?

You have to fill the below given grid in a manner that every row and column contains the digits 1 to 6. Also, make sure that the squares that are connected with each other must contains the same digit.