Answer:
Reaction A, B, E and F are exothermic reactions.
Explanation:
Exothermic reactions are defined as the reactions in which energy of reactants is more than the energy of the products. In these reactions, energy is released by the system.
The total enthalpy of the reaction 
comes out to be negative.
Endothermic reactions are defined as the reactions in which energy of products is more than the energy of the reactants. In these reactions, energy is absorbed by the system.
The total enthalpy of the reaction comes out to be positive.
So, from the given option reaction which are exothermic are with negative value that enthalpy of reaction and those are:
1) 
,ΔH = -1203 kJ/mol
2)
,ΔH =-176 kJ/mol
3) 
,ΔH = -393.5 kJ/mol
4) 
,ΔH =-891 kJ/mol
Activation energy is defined as the least amount of energy that is needed to be available in a chemical system with potential reactants in order to result a chemical reaction. Therefore, the correct answer would be the first option: the heat released in a reaction.
Fluorine is an element with the highest electronegativity value.
Answer:
The solutions are classified according to their ability to scatter light rays.
We can't just use this property because some true solutions also contain undissolved solute.
Explanation:
Tyndall effect refers to the ability of a solution to scatter light rays. True solutions do not scatter light rays while false solutions scatter light rays.
Colloid particles are not large enough to be seen with naked eyes unlike suspensions. We should not confuse a colloid with a suspension because in a suspension, the dispersed solutes are seen with naked eye.
