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Free questions · NEET · Chemistry

Structure of Atom: questions with solutions

3 free questions from this chapter (the full set has 30). Marking: +4 for correct · −1 for incorrect · 0 for unattempted.

Question 1Level 3 · AdvancedSingle correct
In Thomson's model of the atom, which assumption is correctly stated?
AElectrons revolve around the positive charge in fixed circular orbits of definite energy.
BThe positive charge is located at the centre while the electrons are spread uniformly through the atom.
CThe mass of the atom is assumed to be uniformly distributed over the atom, with electrons embedded in a sphere of positive charge.
DMost of the mass of the atom is concentrated in a tiny positively charged centre.
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Answer: C

Key insight: NCERT describes Thomson's atom as a sphere of radius about m in which the positive charge is uniformly distributed and electrons are embedded (plum pudding / raisin pudding / watermelon model), and an important feature is that the MASS of the atom is assumed to be uniformly distributed over the atom. D is Rutherford's nucleus; A is Bohr's postulate; B reverses the model. Trap: D and B sound 'modern' and look attractive. Exam pattern: NEET – features of Thomson's plum-pudding model
Question 2Level 2 · ExamSingle correct
Which statement about cathode rays observed in a discharge tube is INCORRECT?
ATheir characteristics depend on the material of the electrodes and the nature of the gas in the tube.
BThey start from the cathode and move towards the anode.
CIn the absence of electric or magnetic field, they travel in straight lines.
DThey are not visible themselves, but their behaviour can be observed using fluorescent or phosphorescent materials.
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Answer: A

Key insight: NCERT stresses that the characteristics of cathode rays (electrons) do NOT depend on the material of the electrodes or the nature of the gas, which is why electrons were concluded to be a basic constituent of all atoms. C, B and D are NCERT statements. Trap: confusing this with canal rays, whose properties DO depend on the gas. Exam pattern: NEET – discovery of electron and cathode ray properties
Question 3Level 3 · AdvancedSingle correct
In a discharge tube with a perforated cathode, canal rays (anode rays) are studied with different gases. Which conclusion is correct?
AThe charge to mass ratio of the canal-ray particles is the same for all gases, as for cathode rays.
BThe charge to mass ratio of the canal-ray particles depends on the gas present in the tube.
CCanal-ray particles are deflected by electric fields in the same direction as cathode rays.
DThe charge on the canal-ray particles is always equal to the electronic charge in magnitude.
Show answer and solution

Answer: B

Key insight: canal rays are positive ions formed from the gas, so unlike cathode rays their depends on the gas; the smallest and lightest positive ion was obtained from hydrogen (the proton). The charge on the particles is a whole-number multiple of the electronic charge, not always equal to it (D wrong). Being positive, they deflect opposite to cathode rays (C wrong). Trap: A transfers the cathode-ray result. Exam pattern: NEET – discovery of proton, canal rays

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