Consider the following elements

4Be, 9F, 19K, 20Ca

(a) Select the element having one electron in the outer most shell.

(b) Select two elements of the same group.

(c) Write the formula and state the nature of the Compound formed when the element K reacts with an element X of electronic configuration 2, 8, 7.

An organic compound ‘X’ is a liquid at room temperature. It is also a very good solvent and has the molecular formula C₂H₆O. on oxidation ‘X’ gives ‘Y’ which give, break effervescence on reacting with NaHCO₃. X reacts with Y in the presence of conc.H₂SO₄ to give another compound ‘Z’ which has a pleasant smell. Identify X, Y and Z. also write chemical equations to show the formation of Y and Z.

An element ‘A’ belongs to 3rd period and 17th group of the periodic table.

(a) Write atomic number and electronic configuration of ‘A’

(b) State whether A is a metal or a non – metal.

(c) Write the nature of bond formed if A reacts with another element B of electronic configuration 2, 8, 1.

(d) Write the chemical formula of the compound formed.

Explain with the help of labelled diagrams the development that takes place in each of the body parts of a Planaria where the body is cut into three pieces. Name this process and give an example of an organism in which a similar process can be observed.

List any four methods of contraception used by humans. How does the use of three methods have a direct effect on the health and prosperity of a family?