Find : (i) No.of moles in `10^(20)` atoms of `Cu`
(ii) Mass of `200_(8)^(16)O` atoms in amu
(iii) Mass of `100` atoms of `_(7).^(14)N` in gm
(iv) No.of molecules & atoms in `54 gmH_(2)O`
(v) No.of atoms in `88gmCO_(2)` .

Explanation

`(10^(20))/(N_(A))"moles"`
(ii) `"Mass" of 1 _(8).^(16) O "atom" = 16 "amu"`
`"Mass of" 200 _(8).^(16)O "atom" = 16 xx 200 = 3200 "amu"`
(iii) Mass of `1 _(7).^(14)N "atom" =14 "amu" = 14 xx 1.66 xx 10^(-24)g`
Mass of `100_(7).^(14)N "atom" = 1400 xx 1.66 xx 10^(-24)g`
(iv) Molar mass `H_(2)O = 18 g mol^(-1)`
Moles of `H_(2)O` molecule `= (54)/(18) = 3`
no.of molecules in `H_(2)O = 3N_(A)`
no.of atoms in `H_(2)O = 3 xx 3N_(A) = 9N_(A)`
(v) moles of `CO_(2) = (88)/(44) = 2` (Molar mass of `CO_(2) = 44)`
No.of atoms in `CO_(2) = 6N_(A)` .