Consider the following:

1. 1000 litres = 1 m³

2. 1 metric ton = 1000 kg

3. 1 hectare = 10000 m²

Which of the above are correct?

The correct option is 1, 2 and 3.

Let us analyze each statement step-by-step to understand why they are all correct:

1. Analysis of Statement 1: 1000 litres = 1 m³
A litre (L) is a metric unit of volume. One litre is defined as the volume of a cube with side length 10 centimeters (10 cm = 0.1 m).
Therefore, we can express the volume of 1 litre in cubic meters as:

$$1\text{ litre}=(0.1\text{ m}{)}^3=0.001{\text{ m}}^3$$

$$1{\text{ m}}^3=\frac{1}{0.001}\text{ litres}=1000\text{ litres}$$

2. Analysis of Statement 2: 1 metric ton = 1000 kg
A metric ton (often abbreviated as tonne) is a non-SI unit of mass accepted for use with the International System of Units (SI). It is defined precisely as 1000 kilograms (kg).
Therefore, Statement 2 is correct.

3. Analysis of Statement 3: 1 hectare = 10000 m²
A hectare (ha) is a metric unit of area primarily used to measure land. One hectare is defined as the area of a square with side lengths of 100 meters.
We calculate the area in square meters as follows:

$$1\text{ hectare}=100\text{ m}\times 100\text{ m}=10000{\text{ m}}^2$$

Since all three conversion statements are mathematically and scientifically accurate, the correct option is indeed 1, 2 and 3.