Models (Thomson/Rutherford/Bohr), valence, isotopes, ions MCQs

Q1. An atom 'X' has the configuration 2, 8, 6. What is its likely place in the periodic table?

• A.Group 16 (oxygen family), Period 3
• B.Group 6, Period 3
• C.Group 14, Period 3
• D.Group 16, Period 2

Answer: A. Group 16 (oxygen family), Period 3

Which principle settles this? Three shells → Period 3. Six valence electrons → Group 16 (chalcogens). The atom is sulphur. Pick: A) Group 16 (oxygen family), Period 3.

Q2. Which of the following statements is true about a sodium ion (Na+, Z = 11)?

• A.It has 11 protons and 10 electrons
• B.It has 10 protons and 10 electrons
• C.It has 11 protons and 11 electrons
• D.It has 12 protons and 10 electrons

Answer: A. It has 11 protons and 10 electrons

Given 11, asked for the unknown. By Na+ has lost 1 electron: protons = 11, electrons = 10. Na+ has lost 1 electron: protons = 11, electrons = 10. Atomic number Z does not change on ionisation. Hence option A) It has 11 protons and 10 electrons.

Q3. Which of the following correctly describes Thomson's model of the atom?

• A.Electrons are embedded in a positively charged sphere like seeds in a watermelon
• B.Electrons revolve around a small dense nucleus in fixed orbits
• C.Electrons move in waves around the nucleus
• D.All mass is concentrated at the centre and electrons fly around randomly

Answer: A. Electrons are embedded in a positively charged sphere like seeds in a watermelon

That leaves only option A). Confirm with the chapter rule: Thomson visualised the atom as a uniform sphere of positive charge with negatively charged electrons embedded in it - sometimes called the 'plum-pudding' model (chemistry, chapter 'Structure of the Atom'). Answer: A) Electrons are embedded in a positively charged sphere like seeds in a watermelon.