(Relative atomic mass: H = 1, C = 12, N = 14,0 = 16, Na = 23, Cl = 35.5, K = 39, Fe = 56, Pb
= 207; Avogadro constant, N : 6.02 x 1023 mol-'; Molar volume = 22.4 dm' mol-1 at STP or
24 dm' mol-at room conditions)
1. Calculate the molar mass of each of the following substances:
(a) Lead metal, Pb
(c) Sodium nitrate, NaNO,
(b) Chloroform, CHCI,
(d) Iron(III) oxide, FeO,​

answer: c. the experiment shows that the red substance experienced a chemical change.

explanation: chemical change is the change in which chemical composition of the substance changes. physical change is the change in which there is no change in chemical composition.

chemical changes are accompanied by following changes:

a) precipitate formation

b) energy is released or absorbed

c) formation of bubbles

d) change in color

as it is given that the red color has disappeared and there is production of gas, it means the red substance has undergone a chemical change.

e

the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes   ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.