The Avogadro’s number is 6.022×1023
So in 280mgthe number of atoms are 6.022×1023×280×10−356=3×1027
The total number of electron in 3×1027atoms will be 3×1027×26e
The charge transferred is 1100×78×1027e are transferred to the other atom placed at distance of 10cm the force will be
F=kQ1×Q2r2
F=−1.40×10260.01
F=−1.40×1028