NEET Chemistry: The p-Block Elements questions with solutions

Q1. What is the physical state of \( \boldsymbol{P} \boldsymbol{C l} \) late under normal condition?

1. Solid
2. Liquid
3. Gaseous
4. None of these

Answer: Solid

The intended compound is phosphorus trichloride, which is a liquid at room temperature, but the given correct answer says solid, so the question likely refers to a different phosphorus chloride or contains a typo. Under standard chemistry facts, the stated answer is not consistent with PCl3; however, if the exam key marks it as solid, follow the provided key.

Q2. Which of the following statement(s) about the Modern periodic table is/are incorrect? (i) The elements in the Modern periodic table are arranged on the basis of their decreasing atomic number. (ii) The elements in the Modern periodic table are arranged on the basis of their increasing atomic number (iii) Isotopes are placed in an adjoining group(s) in the periodic table.

1. (i) only
2. (i) and (ii)
3. (ii) and (iii)
4. (i) and (iii)

Answer: (i) only

Statement (i) is incorrect because the modern periodic table is arranged in increasing atomic number, not decreasing atomic number. Statement (ii) is correct, and isotopes occupy the same position since they have the same atomic number.

Q3. Match the following: Oxide - Nature (A) CO - Basic (B) BaO - Neutral (C) Al2O3 - Acidic (D) Cl2O7 - Amphoteric Which of the following is incorrect option?

1. (i) (ii) (iv)
2. (ii) (iv) (i)
3. (iv) (iii) (ii)
4. (i) (iii) (iv)

Answer: (i) (iii) (iv)

The incorrect option is (i) (iii) (iv) because CO is neutral, Al2O3 is amphoteric, and Cl2O7 is acidic. BaO is basic, not neutral.

Q4. Which of the following compounds has a 3-centre bond?

1. (a) Diborane
2. (b) Carbon dioxide
3. (c) Boron trifluoride
4. (d) Ammonia

Answer: (a) Diborane

Diborane (B2H6) contains 3-centre-2-electron bonds, also known as banana bonds, where two electrons are shared between three atoms (two boron atoms and one hydrogen atom).

Q5. Among boron trifluoride, stannic chloride and stannous chloride, Lewis acid is represented by:

1. only stannic chloride
2. boron trifluoride and stannic chloride
3. boron trifluoride and stannous chloride
4. only boron trifluoride

Answer: boron trifluoride and stannic chloride

Boron trifluoride (BF3) and stannic chloride (SnCl4) are Lewis acids because they can accept electron pairs. BF3 has an incomplete octet, and SnCl4 has an empty d-orbital for electron pair acceptance.

Q6. The basic structural unit of silicates is:

1. SiO4⁴⁻
2. SiO3²⁻
3. SiO4²⁻
4. SiO

Answer: SiO4⁴⁻

The basic structural unit of silicates is the tetrahedral SiO4⁴⁻ ion, where a silicon atom is surrounded by four oxygen atoms in a tetrahedral arrangement.

Q7. Which statement is wrong?

1. Feldspars are not aluminosilicates
2. Beryl is an example of cyclic silicate
3. Mg2SiO4 is orthosilicate
4. Basic structural unit in silicates is the SiO4 tetrahedron

Answer: Feldspars are not aluminosilicates

Feldspars are aluminosilicates, so the statement in option A is incorrect. The other options correctly describe the respective silicate types and structures.

Q8. Name the type of structure of silicate in which one oxygen atom of [SiO4]⁴⁻ is shared.

1. Linear chain silicate
2. Sheet silicate
3. Pyrosilicate
4. Three dimensional

Answer: Linear chain silicate

In linear chain silicates, one oxygen atom of each [SiO4]⁴⁻ tetrahedron is shared with another tetrahedron, forming a chain-like structure.

Q9. Glass reacts with HF to produce:

1. SiF4
2. H2SiF6
3. H2SiO3
4. Na3AlF6

Answer: H2SiF6

Glass, primarily composed of silica (SiO2), reacts with hydrofluoric acid (HF) to form hexafluorosilicic acid (H2SiF6). This is a well-known reaction in chemistry.

Q10. The substance used as a smoke screen in warfare is:

1. SiCl4
2. PH3
3. PCl5
4. Acetylene

Answer: SiCl4

Silicon tetrachloride (SiCl4) reacts with moisture in the air to produce dense white fumes of hydrochloric acid and silica, making it suitable for use as a smoke screen.

Q11. Roasting of sulphides give the gas X as a by product. This is colorless gas with choking smell of burnt sulphur and caused great damage to respiratory organs as a result of acid rain. Its aqueous solution is acidic, acts as a reducing agent and its acid has never been isolated. The gas X is:

1. SO2
2. CO2
3. SO3
4. H2S

Answer: SO2

The gas X is SO2 (sulfur dioxide), which is produced during the roasting of sulfide ores. It is a colorless gas with a choking smell, forms acidic solutions in water, and acts as a reducing agent. Its acid, H2SO3, is unstable and cannot be isolated.

Q12. Which of the following oxoacids of phosphorus has strongest reducing property?

1. H3PO4
2. H4P2O7
3. H3PO3
4. H3PO2

Answer: H3PO2

H3PO2 (hypophosphorous acid) has the strongest reducing property because it contains one P-H bond, which is responsible for its reducing nature. Other oxoacids lack such P-H bonds.

Q13. Which is the correct statement for the given acids?

1. Phosphinic acid is a diprotic acid while phosphonic acid is a monoprotic acid
2. Phosphinic acid is a monoprotic acid while phosphonic acid is a diprotic acid
3. Both are triprotic acids
4. Both are diprotic acids

Answer: Phosphinic acid is a monoprotic acid while phosphonic acid is a diprotic acid

Phosphinic acid (H3PO2) has only one replaceable hydrogen atom, making it monoprotic, while phosphonic acid (H3PO3) has two replaceable hydrogen atoms, making it diprotic.

Q14. Strong reducing behaviour of H3PO2 is due to

1. presence of one –OH group and two P–H bonds
2. high electron gain enthalpy of phosphorus
3. high oxidation state of phosphorus
4. presence of two –OH groups and one P–H bond

Answer: presence of one –OH group and two P–H bonds

H3PO2 (hypophosphorous acid) is a strong reducing agent because it contains two P–H bonds, which can donate electrons during redox reactions. The presence of these bonds is key to its reducing behavior.

Q15. The product obtained as a result of a reaction of nitrogen with CaC2 is

1. CaCN2
2. CaCN
3. CaC3N3
4. Ca2CN3

Answer: CaCN2

When nitrogen reacts with calcium carbide (CaC2), the product formed is calcium cyanamide (CaCN2). This is a well-known reaction in inorganic chemistry.

Q16. Which of the following oxoacid of sulphur has –O–O– linkage?

1. H2SO4, sulphuric acid
2. H2S2O8, peroxodisulphuric acid
3. H2S2O7, pyrosulphuric acid
4. H2SO3, sulphurous acid

Answer: H2S2O8, peroxodisulphuric acid

H2S2O8 (peroxodisulphuric acid) contains a peroxo (-O-O-) linkage, which is characteristic of its structure. The other options do not have this linkage.

Q17. Identify the correct formula of ‘oleum’ from the following.

1. H2S2O8
2. H2S2O7
3. H2SO3
4. H2SO4

Answer: H2S2O7

Oleum is also known as fuming sulfuric acid and has the chemical formula H2S2O7, which is a mixture of sulfuric acid and sulfur trioxide.

Q18. A compound ‘X’ upon reaction with H2O produces a colorless gas ‘Y’ with rotten fish smell. Gas ‘Y’ is absorbed in a solution of CuSO4 to give Cu3P2 as one of the products. Predict the compound ‘X’.

1. Ca3(PO4)2
2. Ca3P2
3. NH4Cl
4. As2O3

Answer: Ca3P2

The compound 'X' is Ca3P2 (calcium phosphide). When it reacts with water, it produces phosphine gas (PH3), which has a rotten fish smell. Phosphine reacts with CuSO4 to form Cu3P2, confirming the identity of 'X'.

Q19. Which of the following is a nitric acid anhydride?

1. NO
2. NO2
3. N2O5
4. N2O3

Answer: N2O5

Nitric acid (HNO3) is formed when N2O5 reacts with water, making N2O5 its anhydride. Anhydrides are compounds that form acids upon reaction with water.

Q20. More the oxidation state of the central atom (metal), more is its acidity. Hence, SeO2 (O.S. of Se = +4) is acidic. Further for a given O.S., the basic character of the oxides increases with the increasing size of the central atom.

1. Al2O3 and Sb2O3 are amphoteric and Bi2O3 is basic.
2. Since ozone can easily lose oxygen atom (nascent oxygen), it acts as a powerful oxidising agent, and hence, reacts with hydrogen atoms.
3. As the O.N of the central atom of the compounds increases, acidic strength of that compound also increases and on moving from top to bottom in groups acidic strength of oxides also decrease due to decreasing electronegativity in groups.
4. Ozone layer is beneficial to us, because it stops harmful ultraviolet radiations to reach the earth.

Answer: Al2O3 and Sb2O3 are amphoteric and Bi2O3 is basic.

Option A is correct because Al2O3 and Sb2O3 are amphoteric, while Bi2O3 is basic due to the increasing metallic character down the group. The other options are unrelated to the given context of oxidation state and acidity.