question_answer

Atoms consist of electrons, protons and neutrons. If the mass attributed to neutrons were halved and that attributed to the electrons were doubled, atomic mass of \[_{6}^{12}C\] would be approximately: (a) same                              (b) doubled (c) halved                            (d) reduced by 25%

Answer:

The contribution of electrons to the mass of an atom is very little and negligible. \[\therefore \]mass of an atom = mass of protons + mass of neutrons \[=6x+6x\] (\[\because \]mass of neutron\[\approx \]mass of proton) \[\Rightarrow \] \[12=6x+6x=12x\]                          ________ (1) Given that mass attributed by neutron is halved \[\Rightarrow \]the mass contributed by neutrons\[=2x\]. New atomic mass\[=6x+3x=9x\]_______ (2) From (1) and (2), it is clear that atomic mass in second case is reduced by 25%.