84. Which of the following are the discoveries of Einstein?
       (a) Radioactivity and photoelectric effect
       (b) Radioactivity and theory of relativity
       (c) Theory of relativity and photoelectric effect
       (d) x-rays and photoelectric effect
Ans : (c)
85. The emission of an u-particle from a radioactive element:
       (a) decreases the mass number of the nucleide by 2
       (b) decreases the mass number of the nucleide by 4
       (c) increases the mass number of the nucieide by 2
       (d) increase the mass number of the nucleide by 4
Ans : (b)
86. The energy of the winds and the waves is:
       (a) potential
       (b) kinetic
       (c) electrical
       (d) potential and kinetic
Ans : (b)
87. The cleaning of dirty clothes by soaps and detergents is due to a type of molecules called surfactants, which are present in soaps and
     detergents. The surfactant molecules remove the dirt by [CDS 2010]
       (a) making the cloth slippery
       (b) producing some gases between the dirt and the cloth
       (c) dissolving the dirt
       (d) forming some aggregates of themselves and take away the dirt in the core of the aggregates
Ans : (d)
88. A convex mirror makes a good rear-view mirror for a car because:
       (a) it does not form diminished images
       (b) it has no focal point
       (c) its images can be thrown on a screen
       (d) it forms erect, reduced images
Ans : (d)
89. The nuclides having the same number of neutrons but different number of protons or mass number are known as :
       (a) isobars
       (b) isoelectronic
       (c) isotopes
       (d) isotones
Ans : (d)
90. According to the law of conservation of energy,
          1) energy can be created but not destroyed:
          2) energy can neither be created nor destroyed.
          3) energy can be transformed from one form to the other.
       (a) 1 only
       (b) 2 only
       (c) 2 and 3
       (d) 3 only