Which energy state of the triply ionized beryllium (Be+++) has the same electrons orbital radius as that of the ground state of hydrogen? Given Zfor beryllium = 4.


Correct option is

n = 2


for an atom of atomic number Z, the radius of the nth orbit is given by 


Where  is a constant. For the ground state of hydrogen (Z = 1),n = 1 so that    

            r1 = K

let n be the energy state of Be+++ for which the orbital is r1. Putting Z = 4 and rn = r1 = K is eq. (i) we get       




A nucleus  emits one alpha particle and two β-particle The resulting nucleus is


A sample of a radioactive element has a mass of 10g at an instant t = 0. The oppropriate mass of this element in the element in the sample after two mean lives is


If the half lives of a radioactive element that decays in 6 days is 7/8. The fraction that decays in 10 days will be


The wavelength  of de Broglie waves associated with an electron (massm, charger e) accelerated through a potential difference of V is given by (his Planck’s constant)  


A proton, when accelerated through a potential difference of V volts, has a wavelength  associated with it. If an alpha particle ius to have the same wavelength , it must be accelerated through a potential difference of


A proton and an electron move with the same velocity. The associated wavelength for proton is


Two particles of masses m and 2m have equal kinetic energies. Their de Broglie wavelength are in the ratio of 


The wavelength of de Broglie wave associated with a thermal neutron of mass m at absolute temperature T is given by (here k is the Boltzmann constant) 


The momentum of a photon of frequency v is


Which energy state of doubly ionized lithium (Li++) has the same energy as that of the ground state of hydrogen? Given Z for lithium = 3.