1. Tap water
2. Sea water
3. Rainwater
4. Distilled water
Option “3” is correct. Rainwater is purest form of water. Its pH value is 7 .
422. Which gas is known as ‘noble gas”?
1. Hydrogen
2. Oxygen
3. Helium
4. Carbon dioxide
Option “3” is correct. The noble gases make a group of chemical elements with similar properties under standard conditions, they are all odourless, colourless, monatomic gases with very low chemical reactivity. The six noble gases that occur naturally are Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe) and the radioactive Radon (Rn).
423. Assertion (A): Detergent easily removes oil and dirt from dirty garments.
Reason (R) : Detergent increases the surface tension of water.Code :1. Both (A) and (R) are true and (R) is the correct explanation of (A)
2. Both (A) and (R) are true but (R) is not the correct explanation of (A)
3. (A) is true but (R) is false.
4. (A) is false but (R) is true.
Option “3” is correct. Assertion (A) is explained in the above question. The surface tension of water is dramatically reduced by the addition of soap or detergent.
424. Milk is an example of:
1. A gel
2. A foam
3. An emulsion
4. A suspension
Option “3” is correct. An emulsion is a colloid of two or more immiscible liquids where one liquid contains a dispersion of the other liquids. Milk is an example of an emulsion.
425. Which of the following is the procedure for a biogas plant-
Option “4” is correct. Smog is a type of air pollutant. It is composed of nitrogen oxides, sulphur oxides, ozone, smoke or particulates among others (less visible pollutants include carbon monoxide, CFCs and radioactive sources).
428. What is the common name of CaOCl2?
1. Baking Powder
2. Baking Soda
3. Bleaching Powder
4. Washing Soda
Option “3” is correct. Calcium hypochlorite is an inorganic compound with formula CaOCl2. As a mixture with lime and calcium chloride, it is marketed as chlorine powder or bleach powder for water treatment and as a bleaching agent. Common name of is Bleaching Powder.
429. What is the common characteristic of the elements of the same group in the periodic table?
1. Electrons in outer most shell
2. Total number of electrons
3. Total number of protons
4. Atomic weight
Option “1” is correct. The elements in each group have the same number of electrons in the outer orbital. Those outer electrons are also called valence electrons. They are the electrons involved in chemical bonds with other elements.
Option “2” is correct. Nickel allergy is a common cause of allergic contact dermatitis — an itchy rash that appears where your skin touches a usually harmless substance.
is Bleaching Powder.