A singly ionized magnesium atom (A = 24) ion is accelerated to...

The radius of circle formed by a charged particle in a magnetic field perpendicular to the velocity is given by,

$R = \dfrac{mV}{qB} ⇒ R = \dfrac{\sqrt{2mK}}{qB} = \dfrac{\sqrt{2 \times 24 \times 1 . 6 \times {10}^{- 27} \times 5000 \times 1 . 6 \times {10}^{- 19}}}{1 . 6 \times {10}^{- 19} \times 0 . 5} = 979 \times {10}^{- 4}m ≃ 10cm$