What type of ion forms when an atom loses electrons

The right answer is positive ion.

Since the number of protons will be more than the number of electrons and since protons are positively charged, It'l be positively charged as well.  

Those atoms are mainly metals, Hydrogen and Carbon since they tend to lose electrons than gaining in ionic bonding because they have less than three electrons on their outermost energy shells.

an active site is a region that is present on an enzyme where the reactants or the substrate molecules we can say bind and experience a chemical reaction. the substrate is basically a reactant whose concentration is changing and that is converting into a product after binding at the active site of an enzyme