Explain why roots are important for seedlings and the effect of high salt concentration on them.

c) The students would focus on the roots of the seedling.
Reason: Roots are the first part of the seedling to emerge during germination and are responsible for absorbing water and nutrients. High concentrations of sodium chloride in the surrounding solution would create a lower water potential outside the roots, leading to water loss from the root cells via osmosis, thus inhibiting their growth and function.

d) Increasing the concentration of sodium chloride to $2.20 \text{ mol/L}$ would likely cause severe inhibition of growth or even death of the seedling. This is because $2.20 \text{ mol/L}$ is a much higher concentration than those tested, and the previous results showed a significant negative impact on root growth and germination even at lower concentrations ($0.18 \text{ mol/L}$). The extremely high salt concentration would cause excessive water loss from the seedling cells, leading to dehydration and inability to carry out essential metabolic processes.