Science (English Medium) इयत्ता १२ - CBSE Question Bank Solutions for Chemistry

Silicon doped with electron-rich impurity forms ______.

Which of the following statements are true about semiconductors?

(i) Silicon doped with electron-rich impurity is a p-type semiconductor.

(ii) Silicon doped with an electron-rich impurity is an n-type semiconductor.

(iii) Delocalised electrons increase the conductivity of doped silicon.

(iv) An electron vacancy increases the conductivity of n-type semiconductor.

Why are solids incompressible?

Why does the electrical conductivity of semiconductors increase with rise in temperature?

Assertion: Semiconductors are solids with conductivities in the intermediate range from 10^–6 – 10⁴ ohm^–1m^–1.
Reason: Intermediate conductivity in semiconductor is due to partially filled valence band.

Which of the following will show Tyndall effect?

The values of colligative properties of colloidal solution are of small order in comparison to those shown by true solutions of same concentration because of colloidal particles ______.

Which of the following statements are correct?

(i) Mixing two oppositely charged sols neutralises their charges and stabilises the colloid.

(ii) Presence of equal and similar charges on colloidal particles provides stability to the colloids.

(iii) Any amount of dispersed liquid can be added to emulsion without destabilising it.

(iv) Brownian movement stabilises sols.

What happens when a lyophilic sol is added to a lyophobic sol?

(i) Lyophobic sol is protected.

(ii) Lyophilic sol is protected.

(iii) Film of lyophilic sol is formed over lyophobic sol.

(iv) Film of lyophobic sol is formed over lyophilic sol.

Which phenomenon occurs when an electric field is applied to a colloidal solution and electrophoresis is prevented?

(i) Reverse osmosis takes place.

(ii) Electroosmosis takes place.

(iii) Dispersion medium begins to move.

(iv) Dispersion medium becomes stationary.

How does it become possible to cause artificial rain by spraying silver iodide on the clouds?

Why do we add alum to purify water?

What causes brownian motion in colloidal dispersion?

Why does leather get hardened after tanning?

Match the statement given in Column I with the phenomenon given in Column II.

Assertion: An ordinary filter paper impregnated with collodion solution stops the flow of colloidal particles.

Reason: Pore size of the filter paper becomes more than the size of colloidal particle.

Assertion: Colloidal solutions show colligative properties.

Reason: Colloidal particles are large in size.

Assertion: Colloidal solutions do not show brownian motion.

Reason: Brownian motion is responsible for stability of sols.

Assertion: Coagulation power of Al³⁺ is more than Na⁺.

Reason: Greater the valency of the flocculating ion added, greater is its power to cause precipitation (Hardy Schulze rule).

Which of the following are peroxoacids of sulphur?