ICSE Class 10 Chemistry: Periodic Table — Important Questions with Answers 2026

Short Answer Questions (2-3 Marks)

• Q: State the Modern Periodic Law.
  Ans: The Modern Periodic Law states: The physical and chemical properties of elements are periodic functions of their atomic numbers. The modern periodic table arranges elements in order of increasing atomic number.
• Q: What are periods and groups? How many are there in the modern periodic table?
  Ans: Periods are horizontal rows — there are 7 periods. Period number = number of shells. Groups are vertical columns — there are 18 groups. Elements in the same group have similar chemical properties because they have the same number of valence electrons.
• Q: How do the following vary across a period (left to right): (i) atomic size, (ii) metallic character, (iii) electronegativity?
  Ans: (i) Atomic size decreases — nuclear charge increases while shielding remains same, so electrons are pulled closer. (ii) Metallic character decreases — elements tend to gain electrons rather than lose. (iii) Electronegativity increases — atoms attract shared electrons more strongly.
• Q: How do the following vary down a group: (i) atomic size, (ii) ionisation energy, (iii) electron affinity?
  Ans: (i) Atomic size increases — new shells are added, increasing distance from nucleus. (ii) Ionisation energy decreases — outermost electron is farther and shielded, easier to remove. (iii) Electron affinity generally decreases — incoming electron is farther from nucleus, less attracted.
• Q: Define: (i) Ionisation energy, (ii) Electron affinity, (iii) Electronegativity.
  Ans: (i) Ionisation energy: Minimum energy required to remove the outermost electron from an isolated gaseous atom. (ii) Electron affinity: Energy released when an electron is added to an isolated gaseous atom. (iii) Electronegativity: Tendency of an atom to attract shared pair of electrons towards itself in a covalent bond.

Long Answer / Application Questions (4-6 Marks)

• Q: Why are noble gases placed in Group 18? Why are they inert?
  Ans: Noble gases have completely filled outermost shells (stable electronic configuration: ns²np⁶, except He: 1s²). They have no tendency to lose, gain, or share electrons. Hence they are chemically inert and placed in Group 18 (zero valency group).
• Q: An element has atomic number 16. Find its: (i) electronic configuration, (ii) group and period, (iii) metallic or non-metallic nature.
  Ans: (i) Electronic configuration: 2, 8, 6. (ii) Period = number of shells = 3. Group = 10 + valence electrons = 10 + 6 = 16. (iii) It has 6 valence electrons, tends to gain 2 electrons. It is a non-metal (Sulphur).

Exam Tips for This Chapter

• Revise all definitions and laws from Periodic Table — they are commonly asked as 1-2 mark questions
• Practice diagrams related to Periodic Table — neat labelled diagrams carry 2-3 marks
• For numericals, always show formula → substitution → answer with correct units
• Previous year analysis shows Periodic Table carries 8-12 marks in the board exam