Acertain solid substance, that is very hard, has a high melting point and is nonconducting unless melted is most likely to be: a) i₂
b) kcl
c) no₂
d) h₂o
e) cr

B) KCl

Explanation:

It is an odourless gas with a melting point of of 770°c and a boiling point of about 1420°c, it exists in a white crystalline solid form. KCl is highly water soluble and also soluble in other variety of polar solvent but insoluble in many organic solvents.

3 1/4 %

explanation:

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.