The valency of an element with atomic number 13 is: MCQ with Answer and Explanation

Explanation:
Silicon is a metalloid, possessing properties intermediate between metals and non-metals. It has a metallic luster but is brittle and a semiconductor. Other metalloids include boron, germanium, arsenic, antimony, tellurium. Sodium and calcium are metals (good conductors, malleable). Chlorine is a non-metal (gas, poor conductor). Metalloids are found along the zigzag line in the p-block of the periodic table.

Explanation:
Chlorination is the addition of chlorine gas or bleaching powder to water to disinfect it. Chlorine is a strong oxidizing agent that kills pathogenic (disease-causing) bacteria and viruses, making the water safe for drinking. It does not remove hardness or suspended impurities.

Explanation:
Across period 3, S (Z=16) to Cl (Z=17) nuclear charge increases, attracting electron cloud more strongly, reducing atomic radius. Number of shells is same (3).