Statement I : Limestone decomposes when it is heated in air. Statement II : Increase in the content of $\mathrm{CO}_2$ in the atmosphere in recent years is mainly due to the using of limestone in the manufacture of cement.

• Correct answer
  A

  Both the statements are individually true and Statement II is the correct explanation of Statement I.
• B

  Both the Statements are individually true but Statement II is not the correct explanation of Statement I.
• C

  Statement I is true but Statement II is false.
• D

  Statement I is false but Statement II is true.

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