What is the likely reason for the yellow circle of dead grass observed after a salt and ice mixture spills onto it?

The observation of a yellow circle of dead grass after a salt and ice mixture spills onto it can be attributed to the concept of osmotic balance and how plant cells respond to high solute concentrations.

When the salt from the mixture comes into contact with the grass, it creates a hyperosmotic environment. This means that the concentration of solutes (in this case, salt) outside the grass cells is much higher than that inside the cells. As a result, water moves out of the grass cells through osmosis in an attempt to equalize the solute concentrations on both sides of the cell membrane. This loss of water causes the cells to become dehydrated, leading to cell damage and, ultimately, the death of that area of grass. The visible signs include yellowing and dying grass where the salt mixture was applied.

The hyperosmotic conditions created by the salt effectively disrupt the normal water balance in the cells, which is why the plant displays the damage after exposure to the salt and ice mixture.