Question

How many atoms are present in 95.1 L `H_2O` at STP?

Answer 1

You should tell us. What is the state of water at STP?

Explanation:

There are 95.1 kg of water at STP; i.e `(95.1xx10^3*g)/(18.01*g*mol^-1)` `=` `??` `"moles"`.

Now the mole represents Avogadro's number of particles, `6.022xx10^23` `mol^-1`, `N_A`. So multiply the number of moles first by `N_A` to give the number water molecules, and then mulitply this quantity by `3`. Why three?

Because this is a large number, you would be justified in using the symbol `N_A` in your answer, provided you defined it.