Question

if you Sprinkle some common salt on the grass growing on a lawn it is killed the spot. Give reason

Answer 1

because salt destroy the chloropalst present in the grass.

Answer 2

His is due to the flacidity of the crop. The concentration outside the crop or grass is very high than to the concentration of the grass cells on the inside.
Because, of this the phenomenon of osmosis comes into play. Making it flow through the higher concentration outside the grass to the low concentration of salt through a semi-permeable membrane and against the concentration gradient, inside the grasses cellular structure it will make the inside of the cells to become flaccid killing the grass cells and the whole plant on the spot.