The Attractive Force Between Protons and Neutrons in the Nucleus $\pi$

Multiple Choice

The attractive force between protons and neutrons in the nucleus is brought about by the exchange of a virtual pi-meson (m _$\pi$ = 140 MeV/c²) .Estimate the longest time a virtual $\pi$ ⁰ can exist,in accordance with the uncertainty principle $\Delta E \Delta t = \hbar / 2$ .(1 eV = 1.6 *10 ^{- 19} J. )

A) 2.4 *10 ^{- 24} s
B) 6.9 *10 ^{- 27} s
C) 3.3 * 10 ^{- 18} s
D) 2.4 *10 ^{- 21} s
E) 1.6 *10 ^{- 19} s