81.

Which one of the following elements is used in pencil lead?

• Zinc

• Lead

• Carbon (Graphite)

• Tin

A container is first filled with water and then entire water is replaced by mercury. Mercury has a density of 13.6 x 10³ kg/m³ If X is the weight of the water and Y is the weight of the mercury, then

• X = Y

• X = 13.6 Y

• Y = 13.6 X

• None of the above

Density of water is

• maximum at 0°C

• minimum at 0°C

• maximum at 4°C

• minimum at -4°C

The phosphorus used in the manufacture of safety matches is

• Red phosphorus

• Black phosphorus

• White phosphorus

• Scarlet phosphorus

Which one of the following is not a chemical change?

• Ripening of fruits

• Curdling of milk

• Freezing of water

• Digestion of food

One of the main causes of air pollution in cities is emissions from vehicles like cars and trucks. Cars emit various pollutants which are bad for human health when inhaled, like

1. Nitrogen oxides (NO_x)
2. Carbon monoxide (CO)
3. Carbon dioxide (CO₂)
4. Benzene

Which of the above pollutants are not tolerated by human beings even at very low levels?

• 1 and 4 only

• 1 and 2 only

• 1,2 and 3 only

• 1,2 and 3 only

Soap is sodium or potassium salt of

• Stearic acid

• Oleic acid

• Palmitic acid

• All of the above

Mass of a particular amount of substance

1. is the amount of matter present in it.
2. does not vary from place to place.
3. changes with change in gravitational force.

Select the correct answer using the code given below:

• 1,2 and 3

• 1 and 2 only

• 2 and 3 only

• 1 only

Which of the following substances are harmful for health if present in food items?

1. Pesticide residues
2. Lead
3. Metanil yellow
4. Mercury

Select the correct answer using the code given below:

• 1 and 2 only

• 1,2 and 4 only

• 3 and 4 only

• 1,2,3 and 4

An atom of carbon has 6 protons. Its mass number is 12. How many neutrons are present in an atom of carbon?

• 12

• 6

• 10

• 14