Compare hydrogen and halogens on the basis of :(i) Physical state(ii) ion formation(iii) valency(iv) reaction with oxygen

(i) Physical State: Hydrogen is a gas at room temperature. It is the lightest and most abundant element in the universe. On the other hand, halogens can be gases (like Fluorine and Chlorine), liquids (like Bromine), or solids (like Iodine and Astatine) at room temperature.

(ii) Ion Formation: Hydrogen can lose one electron to form a positive ion (H+) or gain one electron to form a negative ion (H-). Halogens, on the other hand, have seven electrons in their outermost shell and tend to gain one electron to achieve a stable electron configuration. This results in the formation of negative ions (X-).

(iii) Valency: Hydrogen has a valency of 1, meaning it can form one bond with another atom. Halogens have a valency of 1 in their negative state (as they tend to gain one electron) and 7 in their positive state (as they can also lose seven electrons).

(iv) Reaction with Oxygen: Hydrogen reacts with oxygen to form water (H2O). The reaction is highly exothermic. Halogens also react with oxygen but the products and reaction conditions vary. For example, fluorine reacts with oxygen to form oxygen difluoride (OF2), while chlorine can react with oxygen to form a variety of compounds including chlorine monoxide (ClO), chlorine dioxide (ClO2), and dichlorine hexoxide (Cl2O6).