Identify the incorrect set from the following

• A

  $\mathrm{SiO}_2$, covalent solid, insulator, high melting point
• Correct answer
  B

  MgO , covalent solid, insulator, high melting point
• C

  $\mathrm{H}_2 \mathrm{O}_{\text {(ice) }}$, molecular solid, insulator, low melting point
• D

  $\mathrm{Ag}(\mathrm{s})$, metallic solid, conductor, high melting point

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