Which element in period 3 on the periodic table is a metalloid? magnesium (mg) aluminum (al) silicon (si) sulfur (s)

Chemical elements exhibit chemical as well as physical properties lie between metals and nonmetals is known as mettaloids.

Metalloids are present on the right hand side of the periodic table such as  boron, silicon, germanium, arsenic, antimony, and tellurium. The series of these six elements is said to be metalloids.

In the attached image, six elements are present in the right side and in grey color are metalloids.  Now, the metalloid which is present in period (from left to right) three on the periodic table is silicon.

Thus, silicon is the correct answer.

hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.  

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.