What is the longest word in the dictionary?

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 is wrong in the below Picture?

Can you count the number of quadrilaterals in the picture below?

John said, "If yesterday was tomorrow, today would be Friday."

When did John make this statement?

Which is faster, Heat or Cold ? Explain.

Can you find the ages of a son, father and grandfather based on the following facts?
The sum of the ages of grandfather, father and son is 140 years.
The age of the son in months is the same as the grandfather in years.
The age of the son in days is the same as the father in weeks.

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

Thirty friends were on a hiking trip when they decided to enjoy the bonfire. They assembled for it and agreed to play a game. For that, they divided themselves into five teams with seven members each, forming five rows.

How did they manage to achieve this formation?

I am a five-letter word and comprises two different vowels and three same consonants. I am so strong that I can spoil your entire work.

Can you find out who am I?