Question

the density of water in 25 degree Celsius is 1.0 gram per ml so how many hydrogen atoms in the 24.4 litre water in the same temperature

Answer 1

The idea here is that you need to use the density of water at 4∘C and the volume of the sample to find its mass, then use water's molar mass to find how many moles of water you get in this sample.

So, density is defined as mass per unit of volume. In this case, a density of `1.00 g/mL tells you that every milliliter of water has a mass of 1.00 g.

This means that 2.46 mL will have a mass of

2.46mL⋅1.00 g1mL=2.46 g

Now, water has molar mass of 18.015 g/mol. This tells you that every mole of water has mass of 18.015 g. In your case, the sample will contain

2.46g⋅1 mole water18.015g=0.1366 moles water

Finally, the relationship between number of moles and number of molecules is given by Avogadro's number, which tells you that every mole of a substance contains exactly 6.022⋅2023 molecules of that substance.

In this case, you will have

0.1366moles⋅6.022⋅1023molecules1mole=8.23⋅1022molecules

So, 2.46 mL of water at a temperature of 4∘C wil contain a total of 8.23⋅1022molecules of water.