It's already too late to plan additional nuclear plants by 1999. A.over
B.at
C.for
D.on

the missing word is for

Explanation:

letter c

The missing word is C. for

Explanation:

Charge on proton, q₁ = e

Charge on alpha particles, q₂ = 2e

The magnetic force is given by :

Here,

For proton, ..........(1)

For alpha particle, ..........(2)

Since, a proton (charge e), traveling perpendicular to a magnetic field, experiences the same force as an alpha particle. So,

So, the ratio of the speed of proton to the alpha particle is 2 : 1 .Hence, this is the required solution.