the shape of impure water meniscus is concave whereas the shape of mercury meniscus is convex , explain
The surface tension of water is less than the surface tension of mercury ( water=0.0727N/m, mercury=0.4355N/m , at 200 C). It means the cohesive force of attraction between water molecules is less than mercury molecules. So, due to less cohesive force the water meniscus is concave and due to greater cohesive force mercury meniscus is convex.