State the similarity of hydrogen with group 1 elements and group 17 elements.

Similarity of hydrogen with group 1 elements:

1. Electronic configuration — Both hydrogen and alkali metals have only one electron in their outermost orbits.
2. Ion formation — Both form a cation by loss of an electron.
   H ⟶ H⁺ + e^-
   Na ⟶ Na⁺ + e^-
3. Valency — Both have the valency 1.
4. Reducing power — Both act as reducing agents.
   CuO + H₂ ⟶ Cu + H₂O
   CuO + 2Na ⟶ Cu + Na₂O
5. Reaction with Oxygen — Both react with oxygen to form respective oxides.
   Hydrogen forms H₂O
   Sodium forms Na₂O

Similarity of hydrogen with group 17 elements:

1. Electronic configuration — Hydrogen and halogens have one electron less than the nearest inert gas.
2. Physical state — Like halogens (fluorine and chlorine), hydrogen too is a gas.
3. Ion formation — Both form an anion by accepting an electron.
   H + e^- ⟶ H^-
   Cl + e^- ⟶ Cl^-
4. Valency — Both have the valency 1.
5. Atomicity — Hydrogen as well as halogens exist in the form of diatomic molecules (H₂, F₂, Cl₂, Br₂, I₂).