In 90 gram of water
a) How many molecules are present in it ?
b) What will be the total number of atoms?
c) What will be the total number of electrons in this sample?

Explanation

a) 90 g water `(H_2 O)
No. of molecules present in = `(90l18) xx N_A`
`=5xx6.022xx10^23`
b) No of atoms present in it
`=`5 xx 6.022xx10^23xx3 = 15 xx 6.022 xx 10^23`
c) No. of electrons in one water molecule =10
`Total no. of electrons in 90g water = total no. of molecule xx 10`
`=5xx6.022xx10^23xx10`
`= 50xx6.022xx10^23`