Pearl is a hard object produced within the soft tissues of a mollusk. Which one of the following is the main constituent of pearl?

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Q: 9 (CDS-II/2017)
Pearl is a hard object produced within the soft tissues of a mollusk.
Which one of the following is the main constituent of pearl?

question_subject: 

Science

question_exam: 

CDS-II

stats: 

0,34,7,34,2,3,2

keywords: 

{'pearl': [0, 0, 0, 1], 'mollusk': [0, 0, 0, 1], 'calcium carbonate': [0, 0, 1, 4], 'calcium oxide': [0, 0, 0, 1], 'calcium': [2, 0, 0, 4], 'calcium sulphate': [0, 1, 1, 7], 'soft tissues': [0, 0, 0, 1], 'main constituent': [0, 0, 1, 0], 'hard object': [0, 0, 0, 1]}

The main constituent of a pearl is calcium carbonate. A pearl is formed within the soft tissues of a mollusk when foreign material, such as a grain of sand, enters the mollusk. The mollusk then secretes layers of calcium carbonate (CaCO3) and a protein called conchiolin, which form the hard outer layer of the pearl.

Calcium carbonate is a common mineral that can be found in many natural materials, including shells, coral, and limestone. It is composed of calcium ions (Ca2+) and carbonate ions (CO3^2-). It provides the structural integrity and hardness to the pearl.

Calcium oxide (CaO), calcium nitrate (Ca(NO3)2), and calcium sulfate (CaSO4) are different chemical compounds that do not play a role in the formation of a pearl. Calcium oxide is a strong base, calcium nitrate is a fertilizer, and calcium sulfate is a common mineral used in various industrial applications.

Therefore, the correct answer is option 1: Calcium carbonate.