Which one among the following statements is not correct about graphite?

• It is the most stable allotrope of carbon

• It is an electrically conducting material

• Crystalline spherical beads of graphite have very good lubricating property under dry conditions

• It is the highest grade of coal

Which one among the following is not a property of salt?

• Salts have ordered packing arrangements called lattices

• Salts have low melting points but high boiling points

• Salts are brittle

• Salts conduct electricity when dissolved in water or even in the molten state

Which among the following statements with regard to pH scale is/are correct?

1. It is a logarithmic scale
2. The scale is limited to 0-14 because the ionic product of water is about 10¹⁴
3. The lower the value of pH the greater is the acidity of the solution

Select the correct answer using the code given below:

• 1 and 2 only

• 1, 2 and 3

• 1 and 3 only

• 2 only

An oxidizing agent is a substance which:

• increases the oxidation number of an element in a given substance

• decreases the oxidation number of an element in a given substance

• is oxidized itself in an oxidation-reduction reaction

• loses electrons in an oxidation reduction reaction

Neutral water with pH about 7 becomes slightly acidic when aerated. This is because:

• oxygen from air is dissolved in the water which makes the water acidic

• dirt, which gets contaminated with the water during aeration makes the water acidic

• ultraviolet radiation dissociates water molecules and makes the water acidic

• carbon-dioxide from air is dissolved

Which one of the following statements is not correct?

• Diesel burns with air in a diesel engine at a high temperature at which nitrogen and oxygen from air can combine whereas petrol burns at a lower temperature at which nitrogen and oxygen can not combine

• Diesel contains some nitrogenous compounds whereas petrol does not

• Nitrogen from air is easily dissolved in diesel but it is not soluble in petrol

• A catalyst is used in diesel engines which contains nitrogen whereas petrol engines do not need such catalysts

Consider the following statements with regard to the properties of water:

1. Water is a good solvent for ionic compound but a poor solvent for a covalent compound
2. Water is a good solvent for covalent compound but a poor solvent for the ionic compound
3. Water has maximum density at the temperature of 277 K

Which of the statements given above are correct?

• 1 and 3 only

• 2 and 3 only

• 1 and 2 only

• 1, 2 and 3

Calcium carbonate is naturally available as limestone and can also be synthesized from quick lime. It is seen that the composition of the elements in both the natural and synthetic calcium carbonate is the same. The validity of which one among the following laws are confirmed by this observation?

• Law of conservation of mass

• Law of definite proportion

• Law of multiple proportions

• Avogadro's law

When aqueous solutions of two salts are mixed, the third salt formed may appear as a solid precipitate or a clear solution depending upon the solubility of its ions. It is observed that all salts of Na, K, NH₄ are soluble. All nitrates and bicarbonates are also soluble. All halides (chlorides, bromides, iodides) are soluble except those of Ag, Hg (I), and Pb. All sulphates are soluble except those of Ag, Ca, Ba and Pb. Which one among the following combinations of solutions will produce a solid precipitate?

• Sodium sulphate and barium chloride

• Magnesium sulphate and barium bicarbonate

• Lithium iodide and barium chloride

• Ammonium sulphate and potassium bromide

A mixture containing SiO₂, NaCl, and NH₄Cl is taken for separating the constituents. The suitable steps required for this are:

• Sublimation-dissolution-filtration-crystallization

• Dissolution-filtration-crystallization-distillation

• Sublimation-evaporation-dissolution-decomposition

• Dissolution-distillation-decomposition evaporation