21.

Why should biodegradable and non-biodegradable wastes be discarded in two separate dust bins?

“A ray of light incident on a rectangular glass slab immersed in any medium emerges parallel to itself.” Draw labelled ray diagram to justify the statement.

“The chromosomes number of the sexually reproducing parents and their offspring is the same.” Justify this statement.

We often observe domestic waste decomposing in the by-lanes of residential colonies. Suggest ways to make people realize that the improper disposal of waste is harmful to the environment. 

List and explain any two advantages associated with water harvesting at community level.

Write the name and the structural formula of the compound formed when ethanol is heated at 443 K with excess of cone. H₂SO₄. State the role of conc. H₂SO₄ in this reaction. Write chemical equation for the reaction. 

Why homologous series of carbon compounds are so called? Write chemical formula of two consecutive members of a homologous series and state the part of these compounds that determines their (i) physical properties, and (ii) chemical properties. 

Given below are some elements of the modern periodic table:             ₄Be, ₉Fe, ₁₄Si, ₁₉K, ₂₀Ca

(i) Select the element that has one electron in the outermost shell and write its electronic configuration.

(ii) Select two elements that belong to the same group. Give reason for your answer.

(iii) Select two elements that belong to the same period. Which one of the two has bigger atomic size?

Write the number of periods the modern periodic table has. How do the valency and metallic character of elements vary on moving from left to right in a period? How do the valency and atomic size of elements vary down a group? 

(a) Explain the process of regeneration in Planaria.                                 (b) How is regeneration different from reproduction?