Question is based on following passage:

p-block elements are placed in groups 13 to 18 of the periodic table. Group 15 is nitrogen family. Nitrogen makes various compounds like \(NH_3\), \(HNO_3\), \(N_2O\), \(NO_2\) etc. Phosphorus exists in the form of white and red phosphorus. White phosphorus glows in dark. \(PH_3\), gas is used as smoke screen. Group 16 is called oxygen family. Dry air contains 21% \(O_2\) gas by volume. Combined sulphur exists as sulphates such as gypsum, epsome salt, baryte etc. The allotropic forms of sulphur are Rhombic and monoclinic sulphur. \(S_2\) is paramagnetic like \(O_2\) and it stable at high temperature. Group 17 is Halogen family. \(F_2\), is highly reactive, \(Cl_2\), is greenish yellow gas. Both \(SO_2\), and \(Cl_2\), are used for bleaching. Group 18 is Noble gas family but some noble gases also form compounds. Complete hydrolysis of \(XeF_6\) gives \(HF\) and \(XeO_3\), as main products.

The permanent bleaching effect is caused by:

Chlorine gas

The correct answer is option 1. Chlorine gas.

Chlorine gas (\(Cl_2\)) is a powerful oxidizing agent commonly used for bleaching in various industries, including paper and textile manufacturing. The bleaching action of chlorine gas is based on its ability to oxidize colored compounds, effectively removing their color.

The working of \(Cl_2\) gas as bleach is as follows:

Oxidation: Chlorine gas acts as an oxidizing agent, meaning it readily accepts electrons from other substances. When chlorine gas comes into contact with colored compounds, it reacts with them by accepting electrons from their molecules. This oxidation reaction alters the chemical structure of the colored compounds, rendering them colorless.

Breakdown of Chromophores: Many colored compounds contain groups of atoms known as chromophores, which are responsible for their color. Chlorine gas breaks down these chromophores through oxidation, disrupting their ability to absorb and reflect light, which results in the loss of color.

Permanent Effect: The bleaching effect caused by chlorine gas is often permanent. Once the colored compounds have been oxidized and their chromophores disrupted, they typically do not revert to their original colored state. This permanence makes chlorine gas a desirable bleaching agent for industries that require long-lasting color removal, such as in the production of white paper or textiles.

Overall, chlorine gas's strong oxidizing properties make it effective for permanently removing color from various substances, thereby achieving a bleaching effect.