A HE^2+ ion travels at right angle to a magnetic field of 0.8Tesla with a velocity of 1x10^5 m/s.
Find the magnitude of the magnetic force on the ion?
F = q V cross B
What is a He^2 ion? Do you mean an He atom with +2 charge ?
if so
charge q = +2*e = 2*1.6*10^-19 = 3.2 * 10^-19 coulombs
v = 10^5 m/s
B = 0.8 T
vectors at right angles so just
multiply