**MCQ’S**

I | a. All above | II | (b) Be , because it is poly electron systm | III | (b) matter contained electrons |

IV | (b) – Ze^{2}/4π€r | V | (d) spin quantum number | VI | (d) 30 |

VII | (d) 662.5 nm | VIII | (c) | IX | (d) radius is 0.529 Å |

X | (a) | XI | (b) | | |

__a) How does Mosley’s Law help in the production of X-rays?__

The mathematical form of Moseley’s law is √v = a (Z – b) Where a and b are constants for a particular metal.

This law states, “The frequency of a spectral line in an X-ray spectrum varies as the square of atomic number of the element emitting it. Thus by proper selection of target material desired X -rays can be produced”.

__b) Which quantum number is also called sub-shell quantum number?__

Azimuthal quantum number tells about the shape of orbital or sub-shell therefore, it is called sub-shell quantum number. It is denoted by “l”. It has value from 0, 1, 2, 3 … (n – 1). The numbers 0, 1, 2, 3 … corresponds for

various subshells

e.g. 0 stands for s-subshell ,1 stands for p- subshell, 2 stands for d- subshell, 3 stands for f- subshell

__c) What is the difference between an orbit and orbital?__

ORBIT | ORBITAL |

It is the circular path on which It is the region in space in which electron revolves around nucleus | It is the region in space in which probability of finding electron is maximum (about 95% ) |

This term is used in the Bohr’s theory of atomic structure and it is two dimensional | This term was coined by quantum mechanical model and it is three dimensional |

Number of electrons in an orbit is Each orbital contains maximum given by the formula, 2n^{2} | The orbital contains maximum two electrons |

__d) What is the relationship between?____a) Energy and wavelength__

The energy of radiation is inversely proportional to its wavelength

E=hc/λ Where E = Energy of radiation λ = wavelength of any light radiation h = Planck’s constant = 6.625 x 10-34 Js

__b) frequency and wavelength__

Frequency is related to wavelength as

c=v/ λ Where or v=c/ λ

c = velocity of light = 3 x 108 ms-1 λ = wavelength of any light radiation

__e) What species are formed by the decay of neutron?__

Free neutron decays into proton with the emission of electron and neutrino.

__f) Hydrogen atom and He+ are mono electronic system, but the size of He+ is much smaller than H, why?__

Both, hydrogen atom and He+ ion have one electron in their outermost shell. However the nucleus of He+ has greater positive charge (due to two protons) than that of hydrogen atom (due to one proton). Therefore, nucleus of He+ attracts its electron more powerfully as compared to hydrogen. Hence, size of He becomes smaller than hydrogen.

__g) How the wavelength of moving particles is inversely proportional to its momentum?__

The wavelength of particles is inversely proportional to its momentum.

λ =h / mv = h/p

Where p = mv = momentum of particle λ= wavelength of any light radiation h= Planck’s constant = 6.625 x 10-34 Js

__h) State Heisenberg’s uncertainty principle.__

It is impossible to determine simultaneously and precisely, both position and momentum of a small fast moving particle e.g. electron.

__i) Why is 4s orbital lower in energy than 3d orbital?__

According to (n+l)rule, the Energy of orbital is determined from the (n+l) value. Lower the (n+l) value lower will be the energy of orbital & vice versa.

Orbital | n+ l Value | n value | The energy value of 4s is lower than 3d |

4s | 4+0 | 4 | |

3d | 3+2 | 5 |

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__j) Write electronic configuration of___{25}Mn^{2+},_{30}Zn^{2+},_{24}Cd^{3+},_{13}Al^{3+}.

__k) What is (n+ l) rule?__