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The rank is : 
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We need to rank the objects according to the magnitude of their momentum.
We know momentum ,
{ here m is mass and v is velocity }
Momentum of object A , 
Momentum of object B , 
Momentum of object C , 
Now, we can rank them in order of their magnitude of momentum .
.
Hence, this is the required solution.
Learn More :
Momentum
brainly.com/question/7957458
Central maximum = d* wavelength/ D
thus
12*10-^3 = 3.4*6.32*10-^7/D
D = 3.4*6.32*10-^7/12*10-^3
D = 1.79*10-^4 m
Dispersion im pretty sure