If inserted into the water as a solid "blob" then it will sink - unless it dissolves first. But, if because of the shape, the mass of water displaced by whole object is greater than the mass of the object, it will float - just as ships made of metal do.
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If an object placed in water sinks - then it has a density greater than water.
A density greater than that of water (which varies with temperature).
The density of an object is its mass divided by its volume. If that is less than the density of water, it will float; if greater it will sink
Normally the water - to float and object has to displace a volume of water equal to its mass. If its density is greater than that of water, the maximum mass of water it can displace is its own volume which, as the water is less dense that it, will have less mass than the object and it will sink. However, for small light objects the surface tension of water comes into play - it is possible to float a steel sewing needle (with a density greater than water) on water by gently dropping a clean needle on its side onto the water surface so that it does not break the surface tension. With a needle floating, adding a few drops of washing up liquid to the surface reduces the surface tension and the needle will then sink.
because salt is higher density than water and dissolves in the water, increasing density