I believe the most appropriate answer would be to change the core from wood to iron. This is because iron is a magnetic material while wood is not magnetic hence cant acquire magnetism. Other factors that would increase the strength of electromagnet would be; increasing the amount of electric current, and increasing the number of windings.
Answer:
The answer to your question is below
Explanation:
Covalent bonds are bonds between to atoms that share a pair of electrons, there are three kinds of covalent bonds but I'll describe only two:
Covalent non polar bond: is a covalent bond between two elements of the same element. Ex two hydrogens, two chlorine, two oxygenes, etc.
Covalent polar bond: is a covalent bond between 2 elements of different elements, for example: hydrogen and chlorine or nitrogen, they are polar because on of the element that form it is smaller than the other one, then a partial positive and a partial negative charge is formed.
Answer: Option (b) is the correct answer.
Explanation:
A covalent compound is defined as the compound in which sharing of electrons take place between the combining atoms. Generally, when two or more non-metals chemically combine together the it will lead to the formation of a covalent compound.
For example, 
and HCl is also a covalent compound.
And, a compound in which transfer of electrons occur between the combining atoms is known as an ionic compound. Whenever, a metal chemically combines with a non-metal then it will always lead to the formation of an ionic compound.
For example, KI is an ionic compound.
Thus, we can conclude that and HCl are the two substances which are covalent compounds.
