An alkaline earth metal '$\mathrm{M}$' readily forms water soluble sulphate and water insoluble hydroxide. Its oxide $\mathrm{MO}$ is very stable to heat and does not have rock-salt structure. $\mathrm{M}$ is

• A

  $\mathrm{Sr}$
• B

  $\mathrm{Ca}$
• C

  $\mathrm{Mg}$
• Correct answer
  D

  $\mathrm{Be}$

Hence, the correct answer is option: 'D'.