Which of the following properties is true for a tooth paste?
- A.It is acidic
- B.It is neutral
- C.It is basic
- D.It is made up of Calcium phosphate, the material of tooth enamel
Correct answer
Explanation
The correct answer is C, it is basic. Toothpaste is mildly basic so that it can neutralise the acid that causes tooth decay.
Bacteria in the mouth break down sugar and food particles left on the teeth and produce acids. When the pH in the mouth falls below about 5.5, the tooth enamel, made of calcium hydroxyapatite (a form of calcium phosphate and the hardest substance in the body), starts to corrode. Brushing with a basic toothpaste neutralises the excess acid and removes the food particles. This example appears in NCERT's chapter on pH in everyday life, along with antacids for acidity and baking soda for stings.
A is wrong because an acidic paste would add to the damage instead of preventing it.
B is wrong because a neutral paste could not neutralise the acid in the mouth.
D is wrong because calcium phosphate is the material of the enamel itself, not what toothpaste is made of; toothpaste is an abrasive, fluoride and detergent paste.
Exam tip: tooth decay starts below pH 5.5; enamel is calcium hydroxyapatite; toothpaste is basic.
Practice Questions
View allWhich one of the following is synthesised in human body that dilates blood vessels and increases blood flow?
- A.Nitric oxide
- B.Nitrous oxide
- C.Nitrogen dioxide
- D.Nitrogen pentoxide
Show answer
The body makes nitric oxide (NO) itself, and it relaxes the walls of blood vessels so that they widen and carry more blood.
Read the full explanation →A stainless steel chamber contains Ar gas at a temperature T and pressure P. The total number of Ar atoms in the chamber is n. Now Ar gas in the chamber is replaced by CO₂ gas and the total number of CO₂ molecules in the chamber is n/2 at the same temperature T. The pressure in the chamber now is P'. Which one of the following relations holds true? (Both the gases behave as ideal gases)
- A.P' = P
- B.P' = 2P
- C.P' = P/2
- D.P' = P/4
Show answer
For an ideal gas in a fixed volume at a fixed temperature, pressure is proportional to the number of molecules, so half the molecules give half the pressure.
Read the full explanation →In which of the following pairs are the ions isoelectronic?
- A.Mg²⁺, Ar
- B.Na⁺, O²⁻
- C.Al³⁺, Cl⁻
- D.K⁺, Ne
Show answer
Both have 10 electrons, the same number as a neon atom, so they are isoelectronic. Isoelectronic species have the same number of electrons.
Read the full explanation →A solid disc and a solid sphere have the same mass and same radius. Which one has the higher moment of inertia about its centre of mass?
- A.The disc
- B.The sphere
- C.Both have the same moment of inertia
- D.The information provided is not sufficient to answer the question
Show answer
About an axis through the centre, a solid disc has I = ½MR² while a solid sphere has I = ⅖MR², and ½ is larger than ⅖.
Read the full explanation →Numerically two thermometers, one in Fahrenheit scale and another in Celsius scale shall read same at
- A.−40°
- B.0°
- C.−273°
- D.100°
Show answer
At this one temperature the Celsius and Fahrenheit scales show the same number. The two scales are linked by F = (9/5)C + 32.
Read the full explanation →