Which of the following is not true about covalent compounds?
a. they are made of molecules and can be gases, liquids or solids
b. they have low melting and boiling points
c. they are good electrical conductors in in all phases
d. many are soluble in nonpolar liquids but not in water

The option C) is not true

Explanation:

The covalent bond is the chemical bond between atoms where electrons are shared, forming a molecule. Covalent bonds are established between non-metallic elements, such as hydrogen H, oxygen O and chlorine Cl. These elements have many electrons in their outermost level (valence electrons) and have a tendency to gain electrons to acquire the stability of the electronic structure of noble gas. The shared electron pair is common to the two atoms and holds them together.

As mentioned, substances that have covalent bonding constitute molecules, that is, clusters of a number of atoms that are linked by covalent bonding. Then option A) is true.

The molecular compounds have melting and low boiling points, since intermolecular forces are very weak compared to intramolecular forces (covalent bonds).Then option B) is true.

They do not conduct electricity in any physical state since the electrons in the bond are strongly located and attracted by the two nuclei of the atoms that share them.´Then the option C) is not true.

Finally you have the solubility. Most are poorly soluble in water because when dissolved in water no ions form. Actually the solubility is dependent on its polarity. Polars are soluble in polar solvents such as water or ethanol, nonpolar solvents in apolar solvents such as benzene or hexane.

electrical power