Non-metals Archives

1. Which one of the following non-metals is present in solid state ?

Which one of the following non-metals is present in solid state ?

Bromine

Boron

Krypton

Radon

This question was previously asked in

UPSC CISF-AC-EXE – 2017

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The correct answer is Boron.

Non-metals exist in various states at room temperature: solid (e.g., Carbon, Phosphorus, Sulphur, Boron), liquid (Bromine), and gas (e.g., Hydrogen, Oxygen, Nitrogen, noble gases like Krypton, Radon). Among the given options, Bromine is a liquid, while Krypton and Radon are gases. Boron is a non-metal (or metalloid often grouped with non-metals) and exists as a solid under standard conditions.

Boron is a brittle, dark, lustrous metalloid. Elemental boron is used in semiconductors and pyrotechnics. Other common solid non-metals include carbon (diamond, graphite), phosphorus (white, red, black forms), sulfur, and selenium.

2. Which one among the following elements is polyatomic ?

Which one among the following elements is polyatomic ?

Phosphorus

Sulphur

Chlorine

Aluminium

This question was previously asked in

UPSC NDA-2 – 2024

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The correct answer is B) Sulphur.

An element is considered polyatomic if its stable molecular form consists of more than two atoms of that element bonded together. Sulphur exists in various allotropes, the most common and stable form being the S₈ molecule, which has a ring structure containing eight sulphur atoms. This makes sulphur a polyatomic element.

Chlorine exists as diatomic molecules (Cl₂). Aluminium is a metal and exists as individual atoms in its elemental state (monatomic in solid form). Phosphorus exists in various allotropes, such as white phosphorus (P₄, tetratomic) and red phosphorus (polymeric). While Phosphorus (P₄) is also polyatomic, Sulphur (S₈) is a common example used to illustrate polyatomic elements in chemistry, and it is explicitly polyatomic in its stable form. Given the options and the need for a single correct answer, S₈ is a clear example of a polyatomic molecule.

3. White Phosphorus glows in the dark due to:

White Phosphorus glows in the dark due to:

amorphous character

slow oxidation

high ignition temperature

good conducting property of electricity

This question was previously asked in

UPSC NDA-2 – 2015

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The correct answer is B) slow oxidation.

White phosphorus exhibits phosphorescence, which is a form of chemiluminescence resulting from its slow oxidation when exposed to air. This process releases energy in the form of light, causing it to glow faintly in the dark. This is often referred to as ‘cold light’.

Amorphous character, high ignition temperature (white phosphorus has a very low ignition temperature, around 30°C), and good electrical conductivity are not the reasons for its glow. Its low ignition temperature makes it highly reactive and dangerous.

4. For manufacturing of glass, which among the following is used as a sou

For manufacturing of glass, which among the following is used as a source of silica ?

Fine clay soil

Wood powder

Coconut shell

Sand

This question was previously asked in

UPSC NDA-1 – 2023

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Glass is primarily composed of silica (silicon dioxide, SiO₂). The main raw material used as a source of silica for glass manufacturing is sand, specifically high-purity silica sand (often called quartz sand). Other components like soda ash (sodium carbonate) and limestone (calcium carbonate) are added to lower the melting point and improve workability.

– Glass is mainly made of silica (SiO₂).
– The primary natural source of silica used in glass manufacturing is sand.
– High purity silica sand is preferred for glassmaking.

Fine clay soil contains silica, but it also contains many impurities (like alumina, iron oxides) that would affect the clarity and properties of the glass. Wood powder and coconut shells are organic materials and not sources of silica for glassmaking.

5. The phosphorus used in the manufacture of safety matches is

The phosphorus used in the manufacture of safety matches is

Red phosphorus

Black phosphorus

White phosphorus

Scarlet phosphorus

This question was previously asked in

UPSC NDA-1 – 2016

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Safety matches utilize red phosphorus. Red phosphorus is a less reactive allotrope of phosphorus compared to white phosphorus. The striking surface of a safety matchbox contains red phosphorus, powdered glass, and a binder. The match head contains oxidizing agents (like potassium chlorate), fuel (like sulfur or antimony trisulfide), and a binder. When the match head is struck against the striking surface, the friction generates heat and converts a tiny amount of red phosphorus to white phosphorus, which ignites spontaneously in the presence of the oxidizing agent on the match head. This then ignites the fuel in the match head, starting the flame.

Red phosphorus is used in safety matches due to its relatively low reactivity and non-toxicity compared to white phosphorus.

White phosphorus is highly toxic and pyrophoric (ignites spontaneously in air), which led to its ban in matches in many countries. Black phosphorus and scarlet phosphorus are other allotropes of phosphorus, but red phosphorus is the one commonly used in safety matches.

6. The valency of phosphorus is

The valency of phosphorus is

2, 3

3, 4

4, 5

3, 5

This question was previously asked in

UPSC CDS-2 – 2020

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Phosphorus commonly exhibits valencies of 3 and 5.

Phosphorus is in Group 15 (VA). In compounds like PH₃ or PCl₃, phosphorus has a valency of 3, using its three unpaired p-electrons for bonding. Due to the presence of vacant d-orbitals, phosphorus can expand its valence shell and form five covalent bonds, as seen in compounds like PCl₅ or P₂O₅, where its valency is 5.

Phosphorus can also exhibit other oxidation states and valencies in specific compounds, but 3 and 5 are the most common valencies.

7. Which of the following characteristics is common to hydrogen, nitrogen

Which of the following characteristics is common to hydrogen, nitrogen, oxygen and carbon dioxide?

They are all diatomic.

They are all gases at room temperature.

They are all coloured.

They all have same reactivity.

This question was previously asked in

UPSC CDS-2 – 2018

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Hydrogen, nitrogen, oxygen, and carbon dioxide are all gases at room temperature.

At standard room temperature (around 20-25 °C) and pressure (1 atm), Hydrogen (H₂), Nitrogen (N₂), Oxygen (O₂), and Carbon Dioxide (CO₂) all exist in the gaseous state.

Option A is incorrect because while H₂, N₂, and O₂ are diatomic, CO₂ is triatomic. Option C is incorrect because all four gases are colourless. Option D is incorrect because they have vastly different reactivities (e.g., flammability, ability to support combustion, inertness).

8. Which one of the following statements is true when non-metals are diss

Which one of the following statements is true when non-metals are dissolved in water ?

They produce basic oxides.

They produce acidic oxides.

They produce neutral oxides.

They provide hydroxides.

This question was previously asked in

UPSC CDS-1 – 2022

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While non-metals themselves generally do not react with water to produce oxides, their oxides (non-metal oxides) are typically acidic oxides. When these acidic oxides dissolve in water, they react to form acidic solutions. For example, CO2 dissolves in water to form carbonic acid, SO2 forms sulfurous acid, and SO3 forms sulfuric acid. Thus, non-metal oxides are characterized as producing acidic solutions when dissolved in water.

Oxides are classified as acidic, basic, amphoteric, or neutral. Non-metal oxides generally react with water to form acids, classifying them as acidic oxides. Metal oxides, in contrast, generally react with water to form bases, classifying them as basic oxides.

Some non-metals like chlorine react with water in a redox process (disproportionation) to form acidic solutions (HCl and HOCl). However, the options provided relate to oxides and hydroxides. The most common and general property associated with non-metals in this context (especially when contrasted with metals forming basic oxides/hydroxides) is the acidic nature of their oxides and the resulting solutions when these oxides dissolve in water.

9. Which one of the following elements is a non-metal but is lustrous ?

Which one of the following elements is a non-metal but is lustrous ?

Carbon

Silicon

Germanium

Iodine

This question was previously asked in

UPSC CDS-1 – 2021

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Iodine is a halogen (Group 17 element) and is classified as a non-metal. However, solid iodine crystals have a distinct metallic lustre (shiny appearance), making it an exception to the general rule that non-metals are non-lustrous.

– Metals are typically lustrous, malleable, ductile, and good conductors of heat and electricity.
– Non-metals are typically brittle, non-lustrous, and poor conductors (except for graphite).
– Iodine exhibits properties characteristic of non-metals (e.g., it forms negative ions, is a poor conductor of electricity in solid form) but stands out for its metallic lustre in solid state.

– Carbon exists in various allotropes; diamond is very lustrous, and graphite has a dull metallic sheen, but elemental carbon is broadly considered a non-metal.
– Silicon and Germanium are metalloids, possessing properties intermediate between metals and non-metals, and they are typically lustrous semiconductors. The question asks for a non-metal.