In Milikan’s experiment, static electric charge on the oil drops has been obtained by shining X-rays. If the static electric charge on the oil drop is –1.282 × 10^–18C, calculate the number of electrons present on it.

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Number of electrons, n \(=\frac { total\ charge\ in\ oil\ drop }{ charge\ on\ 1\ electron } \)
\(=\frac { -1.282\times { 10 }^{ -18 }C }{ -1.6022\times { 10 }^{ -19 }C } =0.800\times 10=8.0\ electrons\)

Explain the physical significance of van derWaals' parameters.

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a is measure of magnitude of intermolecular forces of attraction while b is a measure of the effective volume of the gas molecules.Value of a and b depends upon the characteristics of a gas.

When 430 J of work was done on a system, it lost 120 J of energy as heat.Calculate the value of internal energy change(\(\Delta U\)) for this process.

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+310 J

Does the oxidation number of an element in any molecule or any polyatomic ion represent the actual charge on it?

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No, the oxidation number of an element in any species is an apparent charge on the atom which it appears to have acquired when all other atoms in the species are removed as ions.

Lithium is the only alkali metal that forms nitride directly on reaction with air. Explain.

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Li⁺ ion being small in size can easily stablize small nitride ion N^3-,however other alkali metal ions because of their larger size cannot stablise smaller nitride ion.Thus,only lithium forms nitride.

Explain the nature of boric acid as a Lewis acid in water?

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It is not a protic acid because it does not ionise in H₂ O to give a proton. It acts as a Lewis acis by accepting electrons from a hydroxyl ion of water and in turn releases H⁺ ions.
B(OH)₃ + HOH\(\longrightarrow \)[B(OH)₄]^- + H⁺

Why does benzene undergo electrophilic substitution reactions easily and nucleophilic substitutions with difficulty?

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Due to the presence of delocalised \(6\pi -\)electrons, benzene acts as a rich source of electrons. So, it attracts the electrophilic reagent (electron deficient species) towards itself but repels the nucleophilic reagents. That's why benzene gives electrophilic substitution reactions easily and nucleophilic substitution reaction with difficulty.

One mole of any substance contains 6.022\( \times\)10²³ atoms / molecules.Number of molecules of H₂SO₄ present in 100 mL of 0.02 M H₂SO₄. What will be the solution?

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Write the type of hybridization involved in CH₄ C₂H₄ and C₂H_2.

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What is salt bridge?

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What is drikold and for what purpose it is used?

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1. Give experiments to show that
   Cathode rays consist of material particles.

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2. Use the information and data given below to answer the question, stronger intermolecular forces result in higher boiling point.
   Strength of London forces increases with the number of electrons in the molecules. The boiling point of HF, HCI, HBr, and HI are 293 K, 189 K, 206 K and 238 K respectively.
   Why is the boiling point of hydrogen fluoride highest while that of hydrogen chloride lowest?

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1. What is meant by reaction quotient?

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2. Complete the following reaction  \(2{ K }_{ 4 }\left[ Fe{ \left( CN \right) }_{ 6 } \right] +{ H }_{ 2 }S{ O }_{ 4 }+{ H }_{ 2 }{ O }_{ 2 }\longrightarrow \)

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1. Complete the following reactions.
   \({ O }_{ 2 }^{ - }\)  + H₂ O  \(\longrightarrow \) 

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2. Show the formation of the electrophile in the following reactions
   HNO₃+H₂SO₄

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1. Depending upon the nature of pollutant, how can the pollution be classified into different types?

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What do you understand by 'Representative elements'? Name the groups whose elements are called representative elements.

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