A body of mass 'm' is floating in a liquid of density 'p'.What is the loss of weight of body?

You need to study the principle some more. You don't even have a coherent question.

When you step into water, the water level goes up. Your body displaces water equal to its own volume. The weight of that amount of water pushes UP on your body, as the weight of your body pushes DOWN on the water. If the weight of water displaced equals the weight of your body, you float. If less, then you sink.

Now suppose you want to measure the density of a piece of metal to determine whether it is pure gold. You tie the metal with a fine thread and hang it from a scale. Record the weight. Raise a glass of water so the metal is submerged and record the new weight. Remember the water pushes UP on the metal, so the difference in weight is the weight of water displaced. Convert that weight to a volume and calculate the density, weight/volume. It happens that one cc of water weighs one gram at about four degrees C, so if you are working in grams it's real simple. If the coin is pure gold the density will be close to 19 grams/cc.