There is continuous decrease in atomic radii from Lanthanum (La) to Lutetium (Lu). Give reason. What are its consequences ?

How do the atomic radii vary in group and in period ? Give reasons for variation.

Species diversity decreases as we move away from the equator towards the poles. What could be the possible reasons?

Sketch a graph between frequency of incident radiations and stopping potential for a given photosensitive material. What information can be obtained from the value of the intercept of potential axis? A source of light of frequency of greater than the threshold freuency is placed at a distance of 1 m from the cathode of a photocell? the distnace of hte light sources from the cathode is reduced explain giving reasons, what change will you observe in the Stopping potential.

classically an electron can be in any orbit around nucleus of an atom. Then what determines the typical atomic size? Why is an atom not, say, thousand times bigger than its typical size? Thequestion had greatly puzzled Bohr before he arrived at his famous model of the atom that you have learnt in the text. To simulate what he might well have done before his discovery, let us play as followswith the basic constants of nature e, me, c and see if we can get a quantity with the dimensions of length that is roughly equal to the known size of an atom (~ 10 m).- You will find that the length obtained above is many orders of magnitude smaller than the atomic dimensions. Further, it involves c. But energies of atoms are mostly in non-relativistic domain where c is not expected to play any role. This is what may have suggested Bohr to discard c and look for else h had already made its appearance elsewhere. Bohr lay in recognising that h, m_e , and e will yield the right atomic size. Construct a quantity with the dimension of length from h, me, and e and confirm that its numerical value has indeed the correct order of magnitude.

Read the following passage and answer the questions. Adsorption is surface phenomenon and its differ from absorption, Which occurs throughout the body of the substance which abosorbs. In physisorption, the attractive forces are mainly van der waals forces while in chemisorption actual bonding occuars between the particles of absorbent and absorbate. Generelly, easily liquifying gases are absorved more easily on the surface of a solid as compared to the gases which are liquified with difficulty. Adsorption increases with the increase in pressure and decreases as the temparature is increased. What is the effect of pressure on the extent of adsorption ?

Read the following passage and answer the questions. Adsorption is surface phenomenon and its differ from absorption, Which occurs throughout the body of the substance which abosorbs. In physisorption, the attractive forces are mainly van der waals forces while in chemisorption actual bonding occuars between the particles of absorbent and absorbate. Generelly, easily liquifying gases are absorved more easily on the surface of a solid as compared to the gases which are liquified with difficulty. Adsorption increases with the increase in pressure and decreases as the temparature is increased. What is the effect of temperature on the extent of adsorption ?

As we proceed from La(OH)_3 to Lu(OH)_3 basic strength increases / decreases .

A rain drop of radius 2 mm falls from a height of 500 nr above the ground. It falls with decreasing acceleration (due to viscous resistance of the air) until at half its original height, it attains its maximum (terminal) speed, and moves with uniform speed thereafter. What is the work done by the gravitational force on the drop in the first and second half of its journey ? What is the work done by the resistive force in the entire journey if its speed on reaching the ground is 10 m s^-1 ?

In a hydrogen atom, the electron and proton are bound at a distance of about 0.53 A. (a) Estimate the potential energy of the system in eV, taking the zero of the potential energy at infinite separation of the electron from proton. (b) What is the minimum work required to free the electron, given that its kinetic energy in the orbit is half the magnitude of potential energy obtained in (a)?

Classically, an electron can be in any orbit around the nucleus of an atom. Then what determines the typical atomic size? Why is an atom not, say, thousand times bigger than its typical size? The question had greatly puzzled Bohr before he arrived at his famous model of the atom that you have learnt in the text. To simulate what he might well have done before his discovery, let us play as follows with the basic constants of and see if we can get a quantity with the dimensions of length that is roughly equal to the known of an atom (~ 10^ -10 m).- Construct a quantity with the dimensions of length from the fundamental constants e, m_e , and c. Determine its numerical value.