Which one of the following compounds is not a protonic acid?
A
B(OH)3
B
PO(OH)3
C
SO(OH)2
D
SO2(OH)2
Explanation
B(OH)3 does not provide H+ ions in water
instead it accepts OH– ion and hence it is Lewis
acid.
B(OH)3 + H2O ⇌ [B(OH)4]- + H+
2
MCQ (Single Correct Answer)
AIPMT 2002
Which of the following order is wrong?
A
NH3 < PH3 < AsH3 $$-$$ acidic
B
Li < Be < B < C $$-$$ 1st IP
C
Al2O3 < MgO < Na2O < K2O $$-$$ basic
D
Li+ < Na+ < K+ < Cs+ $$-$$ ionic radius.
Explanation
Along the period, I.P. generally increases but not regularly. Be and B are exceptions. First I.P. increases in moving from left to right in a period, but I.P. of B is lower than Be.
As in case of boron, 2p1 electron have to be removed to get B+(1s2 2s2)
from B(1s2 2s2 2p1), while in case of Be (1s22s2) electron have to be removed to get Be+ (1s22s1). p electron can be removed more easily than s electron so the energy required to remove electron will be less in case of boron.
3
MCQ (Single Correct Answer)
AIPMT 2002
Which of the following statement is true?
A
Silicon exhibits 4 coordination number in its compound.
B
Bond energy of F2 is less than Cl2.
C
Mn(III) oxidation state is more stable than Mn(II) in aqueous state.
D
Elements of 15th group shows only + 3 and +5 oxidation states.
Explanation
Fluorine is more reactive than chlorine. So, bond energy of chlorine is greater than fluorine.
Silicon exhibits 6 coordination numbers.
In aqueous state Mn(II) is more stable.
Mn ⇌ Mn2+ + 2e-
4
MCQ (Single Correct Answer)
AIPMT 2001
Correct order of 1st ionization potential among following elements Be, B, C, N, O is
A
B < Be < C < O < N
B
B < Be < C < N < O
C
Be < B < C < N < O
D
Be < B < C < O < N
Explanation
Be – 1s22s2;
B – 1s22s22p1;
C – 1s22s22p2;
N – 1s22s22p3;
O – 1s22s22p4.
IP increases along the period. But IP of Be > B. Further IP of O < N because atoms with fully or partly filled orbitals are most stable and hence have high ionisation energy.
As in case of boron, 2p1 electron have to be removed to get B+(1s2 2s2)
from B(1s2 2s2 2p1), while in case of Be (1s22s2) electron have to be removed to get Be+ (1s22s1). p electron can be removed more easily than s electron so the energy required to remove electron will be less in case of boron.
Questions Asked from p-Block Elements
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