a.
In solar eclipse moon comes in between earth and sun but it does block all of the radiations of the sun coming to the earth, also that its area its small so it displaces itself from the position after only a few minutes.
in case of lunar eclipse the earth comes between sun and moon, as area of earth is greater than moon, so earth blocks all the light of the sun going to the moon, and it takes much longer time for moon and earth from the position of lunar eclipse.

b.
goiter is caused due to the deficiency of the iodine, and iodine is obtained from sea products like sea food surrounding areas where there is much concentration of iodine in the plants.. but the hilly area people are far away from the sea that why they dont get essential amount of iodine in their food and goiter gets common there.

c.
sodium cholride when mixed with ice decreases its freezing point, so a much more reduced temperature about -20 degree C can be obtained, hence it is used as a freezing mixture.