Chemistry Questions and Answers – P-Block Elements – Oxoacids of Phosphorus

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This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “P-Block Elements – Oxoacids of Phosphorus”.

1. Phosphorus does not form oxoacids.
a) True
b) False
View Answer

Answer: b
Explanation: Similar to the other elements in group 15 of the periodic table, and especially nitrogen, phosphorus does form oxoacids. It forms oxoacids with varying basicity and where the oxidation number pf phosphorus varies too.
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2. What is the range of the oxidation states shown by phosphorus in its oxoacids?
a) +1 to +3
b) +2 to +4
c) +1 to +2
d) +1 to +5
View Answer

Answer: d
Explanation: Phosphorus in the ground state has a valency of 3 and it has a valency of 5 in its excited state. Hence, it forms oxoacids with a wide range of oxidation states where the oxidation states vary from +1 to +5.

3. Which of the following is incorrect about Hypophosphorous acid?
a) It is also called phosphonic acid
b) The oxidation state of phosphorus is +1
c) It is monobasic
d) It is represented by the formula H3PO2
View Answer

Answer: a
Explanation: Hypophosphorous acid, also known as phosphinic acid, is an oxoacid of phosphorus in which, the oxidation state of phosphorus is +1. It is monobasic in nature, that is, it dissociates to produce one hydrogen ion. It is represented by the formula H3PO2.
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4. Orthophosphorous acid can be made from phosphorous trioxide.
a) True
b) False
View Answer

Answer: a
Explanation: Orthophosphorous acid, also known as phosphonic acid, is an oxoacid of phosphorus. It can be prepared by adding phosphorus trioxide (P4O6) to water (H2O) in the ratio 1:6 resulting in the formation of 4 molecules of phosphonic acid.

5. How many P-H bonds does hypophosphorous acid contain?
a) 1
b) 2
c) 3
d) 4
View Answer

Answer: b
Explanation: Hypophosphorous acid, also called as phosphinic acid, has one P – OH bond, 2 P – H bonds and one P = O bond. It is monobasic in nature due to the presence of the one P – OH bond.
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6. What is the basicity of pyrophosphoric acid?
a) Monobasic
b) Tribasic
c) Dibasic
d) Tetrabasic
View Answer

Answer: c
Explanation: Pyrophosphoric acid, represented chemically as H4P2O5, is an oxoacid of phosphorus. It is dibasic in nature. This is due to the presence of two P – OH bonds that are present in the molecule which help release two H+ ions.

7. What is the total number of atoms or groups surrounding each phosphorus atom in its oxoacids?
a) 5
b) 6
c) 3
d) 4
View Answer

Answer: d
Explanation: In all of the oxoacids of phosphorus, the phosphorus atom is tetrahedrally surrounded by four other atoms or groups. The phosphorus atoms can form both double and single bonds in its oxoacids.
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8. What is the oxidation state of phosphorus in hypophosphoric acid?
a) +1
b) +2
c) +3
d) +4
View Answer

Answer: d
Explanation: Hypophosphoric acid, represented chemically as H4P2O6, is an oxoacid of phosphorus. The oxidation state of phosphorus in hypo phosphoric acid is +4. The two phosphorus atoms in total form 4 single bonds with OH group, two double bonds with oxygen and one single bond between the two phosphorus atoms.

9. What is the temperature at which orthophosphoric acid forms pyrophosphoric acid?
a) 673 K
b) 523 K
c) 423 K
d) 700 K
View Answer

Answer: b
Explanation: At a temperature of about 523 K, orthophosphoric acid forms pyrophosphoric acid. At 523 K, two molecules of ortho phosphoric acid (H3PO4) react with each other to form pyro phosphoric acid and water.
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10. Which of the following compounds contain phosphorus with an oxidation state of +5?
a) Peroxodiphosphoric acid
b) Hypophosphorous acid
c) Orthophosphorous acid
d) Hypophosphoric acid
View Answer

Answer: a
Explanation: The oxidation state of phosphorus in peroxodiphosphoric acid is +5. The oxidation state of phosphorus in hypo phosphorus acid is +1, in ortho phosphorous acid is +3 and in hypo phosphoric acid is +4.

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