## Lakshya Education MCQs

Question: The bond dissociation energy of H - H, C - C, and C - H bonds respectively are 104.2, 83.1 and 98.8 kcal/ mole. The electronegativity of C is?
Options:
 A. 2.53 B. 2.51 C. 2.5 D. 2.52
: A

= ECH - EHH×ECC = 98.8 - [(104.2)×(83.1)]12 = 5.75 kcal. (XCH) E.N of C-H bond = 0.218 = 0.218 (5.75)12 = 0.43 XC = 0.43 +XH = 0.43 + 2.1 = 2.53

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## More Questions on This Topic :

Question 1. The elements of groups,1, 2, 13, 14, 15, 16 and 17 are collectively called
1.    Noble gases
2.    Representative or normal elements
3.    Transition elements
4.    Inner transition elements
: B

In the modern periodic table,elements are classified into representative elements, transition elements, inner transition, inner gases based on electronic configuration.

When the group numberof the elements represents the number of valence electrons they arecalledrepresentative elements. Group - 1 (1A) - 1 valence electrons 2 (IIA) - 2 valence electrons 3 (IIIA) - 3 valence electrons 4 (IVA) - 4 valence electrons

15 (VA) - 5 valence electrons

16 (VIA) - 6 valance electrons

17 (VIIA) - 7 valence electrons
Question 2. The correct order regarding the electronegativity of hybrid orbitals of carbon is?
1.    sp < sp2 < sp3
2.    sp < sp2 > sp3
3.    sp > sp2 > sp3
4.    sp > sp2 < sp3
: C

With the increase in % of s-character in hybrid orbitals the electronegativity of the hybrid orbitals increases. sp - 50% s character,

sp2- 33.3 % s character
sp3 - 25% s character.
Question 3. In which block of the modern periodic table the metals, non-metals and metalloids are present all together?
1.    s-block
2.    p-block
3.    d-block
4.    f-block
: B

All the three different types of elements; metals, non-metals and metalloids are present all together in the p-block of the modern periodic table.

Question 4. The cause of periodicity of properties is:
2.    Increasing atomic weights
3.    Number of electrons in the valency orbit
4.    The recurrence of similar outer electronic configuration
: D

The recurrence of similar outer electronic configuration is the reason for the periodicity of properties.

Although Mendeleev discovered that properties were periodic and created a table enlisting the elements, he didn't know the reason behind this occurrence.
Question 5. The ionization energy of F is 320 kJ/mole. The electron gain enthalpy of fluorine would be?
1.    -320 kJ/mole
2.    -160 kJ/mole
3.    320 kJ/mole
4.    160 kJ/mole
: A

Ionization enthalpy is exactly opposite to electron gain enthalpy in this case. If you are talking about ionization enthalpy of F and electron gain enthalpy of F, then we can't say the same thing.

F F + e ΔH=320kJ/mole(I.E) F+e F ΔH=320kJ/mole(I.E)
Question 6. Which of the following is wrong?
1.    Acidic character: NH3
2.    Ionization enthalpy: Li
3.    Basic character: Al2O3