Answer:
1. B, D,
2.A, F
Explanation:
1. According to the law of conservation of mass, In a course of chemical reaction, matter can neither be created nor destroyed but can be changed from one form to another. This means the amount of matter at the begining and ending of a reaction must be thesame.
2. Chemical reaction is not easily reversible. when gas is produced, provided the reaction system is an open system, the gas cannot be recovered and the reactants cannot be recovered from the products. likewise color change are attributed to chemical reaction
Answer:
The correct answer is option c.
Explanation:
Alkanes with higher molecular mass has higher boiling point.
Thisis because when the molar mass of the alkanes increases the the surface area increases with which van der Waals forces between the molecules of alkane also increase which increases the association of the molecules of with each other which results in increase in boiling point is observed.
The increasing order of the molar mass of the given alkanes;

So out of ethane, pentane and heptane . Heptane has highest molecular mass with higher boiling point value. Where as ethane have the lowest value of boiling point.
Answer:
Explanation:
These properties are governed by intermolecular forces. The most important part here is the oxygen interaction with the surroundings. For temperature the decreasing order is pentanol, pentanal and pentane. For viscocity: pentanol, pentanal and pentane. For surface tension: pentanol, pentanal and pentane.
This order, as said before, is due to the interaction of oxygen with the surroundings, within the intermolecular forces we can find van der waals forces and hydrogen bonds, it is also know that H-bonds are stronger than van der waals forces so then that is why we have this type of interactions.
The three steps involve;
Step 1: Separation/expansion of the solute particles
Step 2: Separation/expansion of the solvent particles
Step 3; Combining the solute and solvent particles
The first two steps are usually endothermic. Step 3, nonetheless, can be either exothermic or endothermic and is significant in determining whether the dissolving process will be endothermic or exothermic.
The valence of helium is 0.