The correct option is C mx:ny
Let the two planets be A and B
Planet APlanet BRadiusRARBDensityDADBMassMAMBAccelerationdue togravitygAgB
Acceleration due to gravity of planet A,gA=GMARAgA=GDA×43π R3AR2A=GDA.43πRA (∵ Mass=Density × Volume =D×43πR3)gA=43πGARADA....(i)
Similarly, acceleration due to gravity of planet B, gB=GMBR2BgB=43πGDBRB......(ii)
According to the question:
RARB=xy, DADB=mn
Taking ratio of (i) and (ii):
gAgB=DADB.RARBgAgB=mn.xygA:gs=mx:ny
Hence, the correct answer is option (c).