Exam quizzes

Q.1 The ratio of kinetic energy to the total energy of an electron in a Bohr orbit of the Hydrogen                atom is...?
      A. 2: -1
      B. 1: -1
      C. 1: 1
      D. 1: -2

Explanation:- Based on Bohr's theory, electrostatic force and centripetal forces are equal. So,
                       K(Ze)(e)/r²=mv²/r
                       mv²=K(Ze)(e)/r
                       mv²/2=K(Ze)(e)/2r
                     
Kinetic energy = mv²/2=K(Ze)(e)/2r
Potential energy = -K(Ze)(e)/r
Total energy = KE+PE
                     = -K(Ze)(e)/2r
Hence,the ratio of kinetic energy and the total energy would be 1:-1
Answer :-B

Q.2 The correct order of atomic radii in group 13 element is
       A.B<Ga<Al<Tl< In
       B.B<Al<Ga<In<Tl
       C.B<Al<In<Ga<Tl
       D.B<Ga<Al<In<Tl

Answer:-D

Explanation:-

Q.3 Considering Ellingham diagram,which of the following metals can be used to alumina..?
       A.Mg
       B.Zn
       C.Fe
       D.Cu

Answer:-A

Explnation:-Aluminum's curve lies below most metals thus can act as reducing agent. A given metal oxide can reduce the oxides of other metals whose lines lie above its line on the diagram. Since Magnesium oxide's line lies below Aluminum, Magnesium can tgus reduce Alumina.