Can you find the missing piece of the Porsche?

I am white when I am dirty, and black when I am clean. What am I?

Three ants are going up a hill, one behind the other. The last ant then says to the other ants, 'There is an ant behind me!'' How come?

How many letters are in the alphabet?

How many sides does a circle have?

There is a five-letter word which has 3 consonants(all are same) and 2 different vowels.
Also, something wrong is associated with the word.

Can you name it?

I’m tall when I’m young, and I’m short when I’m old. What am I?

What has one letter and starts with an E?

This is a most unusual paragraph. How quickly can you find out what is so unusual about it? It looks so ordinary, you'd think nothing was wrong with it. Actually, nothing IS wrong with it. But it is not as ordinary as you might think. If you think about it for a bit, you will find out why it is truly so unusual. So what is it? What is so unordinary about this paragraph?

If an electric train is travelling south, then which way is the smoke going?