Which compound, when dissolved in water, conducts electricity and forms a basic solution ?
- A.HCl
- B.CH3COOH
- C.CH3OH
- D.NaOH
Correct answer
Explanation
The correct answer is D, NaOH. Sodium hydroxide dissolves in water and splits completely into Na+ and OH- ions; the ions carry current and the hydroxide ions make the solution strongly basic.
A solution conducts electricity only if it contains free ions. Strong electrolytes such as NaOH ionise fully, so their solutions conduct well. Whether the solution is acidic or basic depends on which ion it produces: H+ (more correctly H3O+) makes it acidic, OH- makes it basic. NaOH, also called caustic soda, turns red litmus blue and has a pH far above 7. It is used to make soap, paper and textiles.
A is wrong because hydrochloric acid conducts electricity but gives H+ ions, so its solution is acidic. B is wrong because acetic acid, the acid of vinegar, is a weak acid; it conducts weakly and its solution is acidic. C is wrong because methanol does not ionise in water, so its solution neither conducts electricity nor is basic.
Exam tip: free ions make a solution conduct; H+ makes it acidic, OH- makes it basic.
Practice Questions
View allWhich one of the following features is an indication for modification of stem of a plant?
- A.Presence of 'eye' on potato
- B.'Scale' found in onion
- C.'Tendril' found in pea
- D.'Hair' present in carrot
Show answer
The eyes of a potato are nodes with buds, and only a stem bears nodes and buds, so they prove that the potato is a modified stem.
Read the full explanation →Which one of the following metals is used in the filaments of photo-electric cells that convert light energy into electric energy ?
- A.Tungsten
- B.Copper
- C.Rubidium
- D.Aluminium
Show answer
Rubidium, an alkali metal like caesium, gives off electrons easily when light falls on it, so it is used in photoelectric cells.
Read the full explanation →Tooth enamel is made up of which one of the following calcium compounds ?
- A.Calcium carbonate
- B.Calcium sulphate
- C.Calcium hydroxide
- D.Calcium phosphate
Show answer
Tooth enamel is made mainly of calcium phosphate in the form of a hard crystal called hydroxyapatite. Enamel is the hardest substance in the human body, harder even than bone.
Read the full explanation →Which one of the following viruses used to be responsible for highly infectious disease Smallpox ?
- A.Adenovirus
- B.Variola virus
- C.Aichi virus
- D.Coxsackie virus
Show answer
Smallpox was caused by the variola virus, a large DNA virus of the pox family that spread from person to person through the air.
Read the full explanation →After fertilization, the fruit and the seed are produced by
- A.ovule and ovary, respectively
- B.ovary and ovule, respectively
- C.ovary, no ovule required
- D.ovule, no ovary required
Show answer
After fertilisation the ovary of the flower grows into the fruit, and each ovule inside it develops into a seed.
Read the full explanation →