1. What is the difference between mass and weight?

For mathematical purposes the mass and the weight are the same.

2. How far is a metre?

A metre was initially defined a one ten millionth of the distance from the equator to the North Pole on a line running through Paris.

It is currently defined as the length of the path travelled by light in a vacuum for a time of 1/299 792 458 th of a second.

3. Which are the most commonly used prefixes?

Kilo − 1000 times the base unit
centi- 1/100th of the basic unit
milli- 1/1000th of the base unit

4. What is a litre?

Think of a litre as a cube of side 10 cm. This gives an volume of 10 × 10 × 10 = 1000cm3

5. What is a tonne?

A tonne is a mass of 1000 kg