Solution:

142857

Explanation:
142857 * 1 = 142857
142857 * 2 = 285714
142857 * 3 = 428571
142857 * 4 = 571428
142857 * 5 = 714285
142857 * 6 = 857142

Note: Such numbers are called cyclic numbers.

Solution:

a) Immediately

Explanation:
"Temperature difference" is the driving force for the heat transfer.
Since the coffee is initially very hot and hence it will be cool down at a very fast rate.
If we add cream immediately : The temperature will initially go down for sure but then will cool down at the slower rate as coffees mixed with cream is cooler than coffee alone and therefore heat cool down rate is less. Also, the cream will increase the mass of the content in the cup and hence larger mass will take more time to cool down.
Hence cream should be added immediately

Solution:

The dead guy is Superman. He died because he was exposed to a Kryptonian rock.

Solution:

Mitch and Irene are the names of hurricane occurred in 2011 and 1998 respectively.

Solution:

Sansa has the siamese (conjoined) twin sister.

Solution:

The answer is very interesting funny but true.
More than 90% of the population is right-handed Since most men's are right handed and they always prefer to dress by own, Therefore if buttons are on the right side they can fasten the button easily.
There is very interesting fact why ladies button on the left-hand side.
When shirts with the button were introduced, it can be afforded only by wealthy men's. These wealth men's wife mostly have maids to dress them up. They dress them by facing the wives and hence its easier for maids to dress the wives if buttons are on the left.

Solution:

Snail (snail foot is a muscle that allows it to move)

Solution:

"EUNOIA" is the shortest(length-6) word that comprises of all vowels.
But many dictionaries does no include this word.

So next comes many seven letter words that contain all vowels.
* SEQUOIA,
* EULOGIA,
* MIAOUED,
* ADOULIE,
* EUDOSIA,
* EUNOMIA
* EUTOPIA
* MOINEAU
* DOULEIA.

EUNOIA means "alertness of brain"

Solution:

It is possible. You have to build a house at south pole and then, all the walls will face the north direction.

Solution:

Both will rotate at Same speed.

Explanation:
Gears of the same size will always rotate at constant speeds despite any smaller or larger gears in between them.