When hydrated cobalt(II) sulfate is heated, it loses water and forms anhydrous cobalt(II) sulfate. All of the water of crystallisation is released into the atmosphere as steam. If $3.10\,\text{g}$ of hydrated cobalt(II) sulfate, $\text{CoSO}_4\cdot x\text{H}_2\text{O}$, is heated until a constant mass is reached, the mass falls by $1.39\,\text{g}$. What is the value of $x$, to the nearest whole number?
- A4
- B6
- C7
- D11