Which of the species kclo2, nh4br, hno2, pbs is/are insoluble in water? 1. nh4br and nh3 2. kclo3 3. hno2 4. all of these 5. pbs?

Solubility rule:   "Like dissolve like"

Reason of insolubility of PbS.

elements make up everything, and they combine to make compounds.

the answer is c

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.