Class 11 Chemistry, Chapter 3 (NCERT). 15 questions by concept. Open “Show answer” for the answer and why.
How to teach this chapter · Common misconceptions & worked visual for this chapter
Why did Mendeleev place iodine after tellurium despite their atomic weights?
(b) That placement preserved similarity with the halogens
Mendeleev prioritized recurring chemical properties over strict mass order.
What did the gaps under aluminium and silicon represent?
(a) Predicted undiscovered elements
Eka-aluminium and eka-silicon were predictions later matched by Ga and Ge.
Mendeleev's periodic law related properties primarily to what quantity?
(a) Atomic weight
The historical law used atomic weight; atomic number became the modern basis.
What evidence did Mendeleev use besides atomic weight?
(d) Similar formulas and chemical properties of compounds
Chemical similarity determined vertical grouping and sometimes overrode strict mass order.
An element ends in 3s²3p⁴. Where is it located?
(b) Period 3, group 16, p block
Highest n is 3, the last subshell is p, and ns²np⁴ corresponds to group 16.
How many columns are in the d block?
(c) 10
Five d orbitals accommodate ten electrons.
Using un=1, bi=2, nil=0, what is the temporary name for Z=120?
(b) Unbinilium
Concatenate the digit roots un-bi-nil and add ium.
What is the systematic symbol corresponding to unbinilium?
(c) Ubn
The symbol uses the initial of each of the three digit roots.
Which property is common among many transition elements?
(d) Variable oxidation states and catalytic behaviour
Partly filled d subshells support characteristic transition behaviour.
Which d-block set is not typical of transition behaviour because of filled d subshells?
(a) Zn, Cd, and Hg
Their common ions retain d¹⁰ configurations and lack many typical properties.
How is covalent radius estimated for a homonuclear single bond?
(b) Half the internuclear distance
Electron clouds lack sharp edges, so an operational half-distance is used.
Which process defines first ionization enthalpy?
(a) X(g) → X⁺(g) + e⁻
The comparison uses isolated gaseous ground-state atoms.
What does a negative electron gain enthalpy mean?
(a) Energy is released when the gaseous atom gains an electron
The sign follows the thermodynamic enthalpy change.
What formula is expected from aluminium and sulphur using Al³⁺ and S²⁻ tendencies?
(b) Al₂S₃
Two Al³⁺ and three S²⁻ give zero net charge.
Why does group-1 reactivity increase down the group?
(c) Increasing radius and shielding make electron loss easier
Lower ionization enthalpy favours cation formation.
Wrong
A chlorine atom is larger than a sodium atom because it has more electrons.
Why it feels right. I assume each extra electron adds another layer.
Right
Across Period 3, added valence electrons enter the same main shell as nuclear charge increases.
Worked example
