Which of the following is the best thermal insulator?

a.) air
b.) water
c.) metal
d.) stone

i’m torn between a and b. i’ve asked many and people say a, but i asked my science teacher and she said b. and also i’ve researched and on answers. com also says water is the better insulator..but idk i’m conflicted! apex

Two charged particles, q1 and q2, are located on the x-axis, with q1 at the origin and q2 initially at x1 = 12.2 mm. in this configuration, q1 exerts a repulsive force of 2.62 µn on q2. particle q2 is then moved to x2 = 18.0 mm. what is the force (magnitude and direction) that q2 exerts on q1 at this new location? (give the magnitude in µn.)