A metallic wire of density d floats horizontally in water . The maximum radius of wire so that it may not sink in water will be ??

Answer 1

Are you intending to ignore surface tension?

I assume not.

surface tension=force/length

force=mg=g*PI*r^2*d*length
let mu be the value of surface tension for water, and as it varies with temperature, look that up.

mu=PIr^2*length*g/length

solve for r.