It is deaf, Dumb and Blind!!!

Still, always tells the truth. What is it?

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

I came first on earth but second on the heaven.
I also came twice in a week but found just once in a year.
I stay away from months but you can find me in February.

What am I?

My friends called me Iron59 because my parents are a chemist and a mathematician. What is my real name?

You have $100 with you and you have to buy 100 balls with it. 100 is the exact figure and you can't go below or above the numbers and you have to use the entire $100. If there is no kind of tax applied how many of each of the following balls will you be able to buy:

Green Balls costing $6
Yellow Balls costing $3
Black Balls costing $0.10

Now, how many of each must you buy to fulfil the condition given?

Decode below three cipher riddles:

26 L of the A
7 D of the W
1000 Y in a M

I inserted a coin in a bottle and closed its mouth with the help of a cork. Now, I was able to take the coin out from the bottle without taking out the cork or breaking the bottle. Can you tell me how I did it?

Find the missing number in the image below.

My thunder comes before the lightning; my lightning comes before clouds; my rain dries all the land it touches. What am I?

There are seven sisters in a house in a village where there is no electricity or any gadget.

Sister-1: Reading Novel
Sister-2: Cooking
Sister-3: Playing Chess
Sister-4: Playing Sudoku
Sister-5: Washing clothes
Sister-6: Gardening

what is Sister-7 doing ?