A compound has the following composition by weight , `Na = 18.60 %, S = 25.80 %, H = 4.02 %" and "O = 51.58 %` Assuming that all the hydrogen atoms in the compound are part of water of crystallization, the correct molecular formula of the compound is

Explanation

Step I. Calculation of empirical formula:

Thus, the simple ratio of Na : S : H : O is 1 : 1 : 5 : 4. Therefore, the empirical formula of the compound is `NaSH_(5)O_(4)`.
Step II. Calculation of molecular formula
Empirical formula mass = `23 + 32 + 5 xx 1 + 4 xx 16 = 124`
Molecular mass = 248
`n=("Molecular mass")/("Empirical formula mass") = 248/124 =2`
`therefore` Molecular formula `=(NaSH_(5)O_(4))_(2)`
`=Na_(2)S_(2)H_(10)O_(8)`
Since all the 10 hydrogen atoms are present as water molecules `H_(2)O`, the total number of water molecules is `5H_(2)O`.
Molecular formula = `Na_(2)S_(2)O_(3).5H_(2)O`