About this quiz
55 questions covering every section of the note on states of matter, mixtures, atoms, acids, bases and pH, indicators, metals, common chemical formulas, rusting and important gases.
This Lok Sewa practice set has 55 multiple-choice questions (Subject: Science and Technology · For: Kharidar, Nayab Subba, Section Officer · Level: Easy). Take the quiz above first; after that, use the study list below to revise every question with its correct answer and a short explanation.
Study list: all 55 questions with answers and explanations
Naphthalene balls kept in clothes slowly disappear without leaving any liquid. What is this change called?
- A) Evaporation
- B) Sublimation ✔
- C) Condensation
- D) Melting
Why: A solid that turns directly into gas without becoming a liquid undergoes sublimation, like camphor and iodine.
Which state of matter has a fixed volume but takes the shape of its container?
- A) Liquid ✔
- B) Solid
- C) Gas
- D) Plasma
Why: A liquid keeps its volume but flows to take the shape of whatever holds it.
Which of the following is a compound?
- A) Air
- B) Oxygen
- C) Water ✔
- D) Soil
Why: Water is formed when hydrogen and oxygen combine chemically in a fixed ratio; air and soil are mixtures and oxygen is an element.
Which method is used to get pure drinking water from salty water?
- A) Filtration
- B) Decantation
- C) Using a magnet
- D) Distillation ✔
Why: In distillation the water is boiled and its vapour is cooled back into pure water, leaving the salt behind.
Which particle of an atom carries a negative charge?
- A) Proton
- B) Electron ✔
- C) Neutron
- D) Nucleus
Why: Electrons are negatively charged and move around the nucleus; protons are positive and neutrons have no charge.
Who discovered the neutron?
- A) J. J. Thomson
- B) John Dalton
- C) James Chadwick ✔
- D) Niels Bohr
Why: James Chadwick discovered the neutron in 1932; J. J. Thomson discovered the electron in 1897.
An atom of sodium has atomic number 11 and mass number 23. How many neutrons does it have?
- A) 12 ✔
- B) 11
- C) 23
- D) 34
Why: Neutrons = mass number − atomic number = 23 − 11 = 12.
Atoms of the same element having the same atomic number but different mass numbers are called what?
- A) Compounds
- B) Alloys
- C) Ions
- D) Isotopes ✔
Why: Isotopes differ only in the number of neutrons; protium, deuterium and tritium are isotopes of hydrogen.
Which acid is found in curd?
- A) Lactic acid ✔
- B) Citric acid
- C) Acetic acid
- D) Tartaric acid
Why: Curd and sour milk contain lactic acid; citric acid is in lemon and acetic acid in vinegar.
The sting of an ant or of a nettle (sisnu) plant contains which acid?
- A) Malic acid
- B) Formic acid ✔
- C) Hydrochloric acid
- D) Oxalic acid
Why: Ant and nettle stings inject formic acid, which causes the burning pain.
What is formed when an acid reacts with a base?
- A) Only gas
- B) Only acid
- C) A metal and oxygen
- D) Salt and water ✔
Why: This reaction is called neutralization and its products are salt and water.
Milk of magnesia is taken to relieve acidity in the stomach. Why does it work?
- A) It is a strong acid
- B) It is neutral like water
- C) It is a base that neutralizes extra stomach acid ✔
- D) It kills all stomach germs
Why: Milk of magnesia (magnesium hydroxide) is a base, so it neutralizes excess hydrochloric acid in the stomach.
A solution has a pH of 3. What is its nature?
- A) Basic
- B) Acidic ✔
- C) Neutral
- D) Strongly basic
Why: Any pH less than 7 is acidic, so a pH of 3 shows an acidic solution.
The pH of human blood is about how much?
- A) 7.4 ✔
- B) 2
- C) 5
- D) 12
Why: Blood is slightly basic with a pH of about 7.4.
What colour does phenolphthalein show in a basic solution?
- A) Red
- B) Colourless
- C) Pink ✔
- D) Yellow
Why: Phenolphthalein stays colourless in acid and turns pink in a base.
Litmus, a common indicator, is obtained from what?
- A) Turmeric
- B) Red cabbage
- C) Rose petals
- D) Lichens ✔
Why: Litmus is a natural dye taken from lichens.
Which is the only metal that is liquid at room temperature?
- A) Sodium
- B) Bromine
- C) Mercury ✔
- D) Aluminium
Why: Mercury is the liquid metal; bromine is also liquid but it is a non-metal.
Which non-metal is a good conductor of electricity?
- A) Graphite ✔
- B) Sulphur
- C) Iodine
- D) Diamond
Why: Graphite, a form of carbon, conducts electricity even though it is a non-metal; diamond does not.
Why are sodium and potassium kept under kerosene?
- A) To make them shiny
- B) Because they react strongly with air and water ✔
- C) To keep them cool
- D) To make them soft
Why: These metals react quickly with moisture and oxygen in air, so kerosene keeps air and water away from them.
Brass is an alloy of which metals?
- A) Copper and tin
- B) Iron and carbon
- C) Iron and chromium
- D) Copper and zinc ✔
Why: Brass is made of copper and zinc; bronze is copper and tin.
What is the chemical formula of baking soda?
- A) NaHCO₃ ✔
- B) Na₂CO₃
- C) NaCl
- D) NaOH
Why: Baking soda is sodium hydrogen carbonate, NaHCO₃; Na₂CO₃ is sodium carbonate (washing soda without its water) and NaOH is caustic soda.
Which substance is used to set broken bones and make statues?
- A) Bleaching powder
- B) Quicklime
- C) Plaster of Paris ✔
- D) Washing soda
Why: Plaster of Paris (CaSO₄·½H₂O) sets hard when mixed with water, so it is used for casts and statues.
What is the chemical name of quicklime?
- A) Calcium carbonate
- B) Calcium oxide ✔
- C) Calcium hydroxide
- D) Calcium sulphate
Why: Quicklime is calcium oxide (CaO); calcium hydroxide is slaked lime and calcium carbonate is limestone.
Galvanization protects iron from rusting by coating it with which metal?
- A) Tin
- B) Copper
- C) Silver
- D) Zinc ✔
Why: In galvanization a layer of zinc covers the iron, as on galvanized roofing sheets.
Biogas (gobar gas) used for cooking in Nepali villages is mainly made of which gas?
- A) Butane
- B) Carbon monoxide
- C) Methane ✔
- D) Nitrogen
Why: Biogas is mainly methane; LPG in cylinders is mainly butane and propane.
Change of a solid directly into gas is called:
- A) Sublimation ✔
- B) Evaporation
- C) Condensation
- D) Melting
Why: E.g. naphthalene, camphor.
Which state of matter has neither fixed shape nor fixed volume?
- A) Gas ✔
- B) Solid
- C) Liquid
- D) None
Why: Gas.
Which of these is a mixture?
- A) Air ✔
- B) Water
- C) Salt
- D) Carbon dioxide
Why: Air is a mixture of gases.
The chemical formula of water is:
- A) H2O ✔
- B) CO2
- C) NaCl
- D) H2O2
Why: Two H, one O.
The chemical formula of common salt is:
- A) NaCl ✔
- B) KCl
- C) CaCO3
- D) NaOH
Why: Sodium chloride.
The positively charged particle of an atom is the:
- A) Proton ✔
- B) Electron
- C) Neutron
- D) Photon
Why: Proton.
Atoms with the same mass number but different atomic numbers are:
- A) Isobars ✔
- B) Isotopes
- C) Isomers
- D) Ions
Why: Isobars.
Which acid is found in lemons?
- A) Citric acid ✔
- B) Lactic acid
- C) Acetic acid
- D) Formic acid
Why: Citric.
Vinegar contains:
- A) Acetic acid ✔
- B) Citric acid
- C) Tartaric acid
- D) Oxalic acid
Why: Acetic acid.
Tamarind contains:
- A) Tartaric acid ✔
- B) Lactic acid
- C) Formic acid
- D) Citric acid
Why: Tartaric.
Which acid is present in car batteries?
- A) Sulphuric acid ✔
- B) Hydrochloric acid
- C) Nitric acid
- D) Acetic acid
Why: H2SO4.
Bases turn red litmus:
- A) Blue ✔
- B) Red
- C) Green
- D) Yellow
Why: Acids turn blue litmus red.
A solution with pH 7 is:
- A) Neutral ✔
- B) Acidic
- C) Basic
- D) Salty
Why: Pure water.
A solution with pH 12 is:
- A) Strongly basic ✔
- B) Strongly acidic
- C) Neutral
- D) Weakly acidic
Why: Above 7 is basic.
Caustic soda is:
- A) Sodium hydroxide ✔
- B) Sodium carbonate
- C) Sodium bicarbonate
- D) Calcium oxide
Why: NaOH.
Washing soda is:
- A) Sodium carbonate ✔
- B) Sodium bicarbonate
- C) Sodium chloride
- D) Calcium carbonate
Why: Na2CO3.
Bleaching powder is:
- A) Calcium oxychloride ✔
- B) Sodium chloride
- C) Calcium carbonate
- D) Potassium nitrate
Why: CaOCl2.
Limestone and marble are mainly:
- A) Calcium carbonate ✔
- B) Calcium sulphate
- C) Sodium carbonate
- D) Magnesium oxide
Why: CaCO3.
The best conductor of electricity among metals is:
- A) Silver ✔
- B) Copper
- C) Aluminium
- D) Iron
Why: Silver; copper is used for cost.
Bronze is an alloy of:
- A) Copper and tin ✔
- B) Copper and zinc
- C) Iron and carbon
- D) Lead and tin
Why: Bronze.
Steel is mainly an alloy of:
- A) Iron and carbon ✔
- B) Copper and zinc
- C) Aluminium and tin
- D) Lead and iron
Why: Steel.
Stainless steel contains iron, carbon and:
- A) Chromium (and nickel) ✔
- B) Gold
- C) Lead
- D) Tin
Why: Chromium prevents rust.
Rust is chemically:
- A) Hydrated iron oxide ✔
- B) Iron sulphate
- C) Iron chloride
- D) Pure iron
Why: Fe2O3·xH2O.
The main gas in biogas is:
- A) Methane ✔
- B) Oxygen
- C) Nitrogen
- D) Hydrogen
Why: CH4.
LPG mainly contains:
- A) Butane and propane ✔
- B) Methane only
- C) Hydrogen
- D) Oxygen
Why: Cooking gas.
Dry ice is solid:
- A) Carbon dioxide ✔
- B) Water
- C) Nitrogen
- D) Oxygen
Why: CO2.
The gas used in fire extinguishers is:
- A) Carbon dioxide ✔
- B) Oxygen
- C) Hydrogen
- D) Chlorine
Why: CO2.
Hard water contains salts of:
- A) Calcium and magnesium ✔
- B) Sodium only
- C) Potassium
- D) Iron only
Why: Ca and Mg.
Which element is used in pencils (lead)?
- A) Graphite (carbon) ✔
- B) Lead
- C) Silicon
- D) Tin
Why: Graphite.
The hardest natural substance is:
- A) Diamond ✔
- B) Graphite
- C) Iron
- D) Quartz
Why: Diamond, a form of carbon.