Question

The marble statues often slowly get corroded when kept in open for a long time. Explain.

Answer 1

When a metal is naturally converted to a more stable form of it like its oxide, sulphide or hydroxide state and leads to the deterioration of the material is known as corrosion. The corrosion of marble is also known as marble cancer.

Complete step by step answer:
Marble is an inorganic chemical compound and is known by the chemical name calcium carbonate having formula as $CaC{o_3}$. Marble is used in cemetery markers, soil treatment, brightener and in making buildings, monuments and statues.
The marble statues often slowly get corroded when kept in air for a long time. This is because the marble does react with the acidic compounds which are present in the air, like carbonic acid, sulphuric acid and nitric acid etc. these compounds can mix with water, oxygen and other chemicals to form more acidic pollutants. This also leads to the acid rain. When the sulphureous, sulphuric and nitric acids present in the polluted air or rain, they do react with the calcite present in the marble.
The acids or the oxides which were present in air but got converted into acids by absorbing moisture from air, react with marble and the reaction can be written as:

$CaC{O_3}\left( {calcium{\text{ }}carbonate} \right) + {H_2}S{O_4}\left( {sulphuric{\text{ }}acid} \right) \to CaS{O_4}\left( {calcium{\text{ }}sulphate} \right) + {H_2}O\left( {water} \right) + C{O_2} \uparrow \left( {carbon{\text{ }}dioxide} \right)$

Even, the wet or dry deposition of the sulphur dioxide on the marble, significantly increases the rate of corrosion.

Note:
The common examples of some monuments and statues which are damaged by corrosion are – Taj Mahal in India, The Thomas Jefferson Memorial in Washington, Leshan Giant Buddha in China etc.