Can you replace the question mark with the correct number?

You are in a room that has three switches and a closed door. The switches control three light bulbs on the other side of the door. Once you open the door, you may never touch the switches again. How can you definitively tell which switch is connected to each of the light bulbs?

What number comes next in this sequence:
7 8 5 5 3 4 4 _

Can you fill the blank with the correct number?

6 30 870 756030 _____

They are three errirs in this question. Can you find them?

You visit a home for specially-abled children on the occasion of Christmas where you meet with 50 children. You have a box of chocolates containing 50 chocolates exactly.

What if you were asked to one chocolate to each child in a manner that one chocolate still remains in the box? Is it possible?

Complete the series by replacing "?" with the correct number.

ST ND RD TH '?'

A chess tournament is taking place on knock-out terms (the one who loses the match is out of the game).
(a) If 10 matches are played in total, how many players participated?
(b) If 20 players took part in the tournament, how many matches were played?

What makes this number unique: 8,549,176,320?

Use only one mathematical symbol and all numbers (0-9) to get a sum of 99