The number of molecules present in 1 litre of water is (assume its density to be 1g/mL)

Sure, here's how you can calculate the number of molecules in 1 litre of water:

1. First, we need to know the molecular weight of water (H2O). The atomic weight of Hydrogen (H) is approximately 1 gram/mole and Oxygen (O) is approximately 16 grams/mole. So, the molecular weight of water (H2O) is approximately 18 grams/mole (12 + 161).

2. Next, we need to convert the volume of water from litres to grams. Given that the density of water is approximately 1 gram/mL, 1 litre (or 1000 mL) of water would weigh approximately 1000 grams.

3. Now, we can calculate the number of moles in 1000 grams of water. We do this by dividing the weight of the water by the molecular weight of water. So, 1000 grams / 18 grams/mole = approximately 55.56 moles.

4. Finally, we can calculate the number of molecules by multiplying the number of moles by Avogadro's number (approximately 6.022 x 10^23 molecules/mole). So, 55.56 moles * 6.022 x 10^23 molecules/mole = approximately 3.34 x 10^25 molecules.

So, there are approximately 3.34 x 10^25 molecules in 1 litre of water.