NCERT Class X Science Class: Chapter –5. Periodic Classification of Elements – Part-8

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Question 39:

Arrange the following elements in the increasing order of their metallic character

Answer:

As we down the group, metallic character increase and a s moving left to right metallic character decrease.

So above in the correct order of increase metallic character.

Question 40:

Identify the elements with the following property and arrange them in increasing order of their reactivity

  1. An element which is a soft and reactive metal

  2. The metal which is an important constituent of limestone

  3. The metal which exists in liquid state at room temperature

Answer:

(a) An element, which is a soft and reactive metal:

An element which is soft and reactive metal is sodium (Na) potassium (K) as alkali metals are soft and reactive.

(b) The metal, which is an important constituent of limestone:

Limestone is calcium carbonate CaCO3. The important constituent of limestone is calcium (Ca).

(c) The metal, which exists in liquid state at room temperature:

Metal which exists in liquid state at room temperature is mercury (Hg)So the increasing order of their reactivity Mercury < Calcium < Sodium < potassium or

Question 41:

Properties of the elements are given below. Where would you locate the following elements in the periodic table?

  1. A soft metal stored under kerosene

  2. An element with variable (more than one) valency stored under water.

  3. An element which is tetravalent and forms the basis of organic chemistry

  4. An element which is an inert gas with atomic number 2

  5. An element whose thin oxide layer is used to make other elements corrosion resistant by the process of “anodizing”

Answer:

  1. A soft metal stored under kerosene:

    Sodium (Na) Group 1 and Period 3 or Potassium (K) Group 1 and Period 4

  2. An element with variable (more than one) valency stored under water:

    Phosphorus (P) Group 15 and Period 3

  3. An element which is tetravalent and forms the basis of organic chemistry:

    Carbon (C) Group 14 and Period 2

  4. An element which is an inert gas with atomic number 2:

    Helium (He) Group 18 and Period 1

  5. An element whose thin oxide layer is used to make other elements corrosion resistant by the process of “anodizing”:

Aluminium (Al) Group 13 and Period 3

Long Answer Questions

Question 42:

An element is placed in 2nd Group and 3rd Period of the Periodic

Table, burns in presence of oxygen to form a basic oxide.

  1. Identify the element

  2. Write the electronic configuration

  3. Write the balanced equation when it burns in the presence of air

  4. Write a balanced equation when this oxide is dissolved in water

  5. Draw the electron dot structure for the formation of this oxide

Answer:

Image electron dot structure for

Image Electron Dot Structure For

Image electron dot structure for

Question 43:

An element X (atomic number 17) reacts with an element Y (atomic number 20) to form a divalent halide.

  1. Where in the periodic table are elements X and Y placed?

  2. Classify X and Y as metal (s), non-metal (s) or metalloid (s)

  3. What will be the nature of oxide of element Y? Identify the nature of bonding in the compound formed

  4. Draw the electron dot structure of the divalent halide

Answer:

  1. X belongs to Group 17 and 3rd period

  2. Y belongs to Group 2 and 4th period

  3. X — Non-metal and Y — Metal

  4. Basic oxide; Ionic bonding

Image electron dot structure of the divalent halide

Image Electron Dot Structure of the Divalent Halide

Image electron dot structure of the divalent halide