Calcium is obtained by the

${\mathrm{CaCO}}_3\stackrel{\mathrm{Roasting}}{\to }\mathrm{CaO}+{\mathrm{CO}}_2$
Heating of chemical substance in presence of "O₂" is called roasting.
→Electrolysis of aqueous CaCl₂ solution
CaCl₂ → Ca⁺² + 2Cl^-
2H₂O → 2H⁺ + 2OH^-
order of reduction potentials of cations : H⁺ > Ca⁺²
order of oxidation potentials of anions : Cl^- > OH^-
At anode : 2Cl^- → Cl₂↑ + 2e^_¯
At cathode : 2H⁺ + 2e^-→ H₂↑

${\mathrm{Ca}}^{+2}+2{\mathrm{OH}}^{-}\stackrel{ }{\to }\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$

Products : Cl₂,H₂,Ca(OH)₂
As reduction potential of H⁺ > Ca⁺² , therefore H₂ is liberated at cathode , but  no deposition of Ca-metal.
4) Electrolysis of Molten anhydrous CaCl₂
$$\begin{gathered} {\mathrm{CaCl}}_{2\left(\mathrm{S}\right)}\stackrel{melting point}{\to }\underset{\mathrm{Molten} \mathrm{state}}{{\mathrm{CaCl}}_{2\left(\mathrm{l}\right)}} \\ {\mathrm{CaCl}}_{2\left(\mathrm{l}\right)}\stackrel{\mathrm{Electrolysis}}{\to }{\mathrm{Ca}}^{+2}+2{\mathrm{Cl}}^{-} \end{gathered}$$

At anode : 2Cl¯ → Cl_2(g)↑ + 2e¯
At cathode : Ca⁺² + 2e¯ → Ca_(s)
Electrolysis of molten CaCl₂ gives "Ca" at cathode