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?
(i) 19K has one electron in the outermost shell and its electronic configuration is 2 8 8 1.
(ii) 4Be and 20Ca belongs to same group i.e., Group-2.
Electronic configuration of Ca and Be is:
4Be - 2 2
20Ca- 2 8 8 2
The number of electrons in the outermost shell of 4Be and 20Ca is same hence they belong to the same group.
(iii) 9F and 4Be belongs to the same period, Period 2.
Electronic configuration:
9F - 2 7
4Be - 2 2
4Be has bigger atomic size then 9F because the atomic radius decreases as we move from left to right. From left to right along a period, the nuclear charge increases and pulls the electrons closer to the nucleus. So, size of F decreases.
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?