In the periodic table,the valency of elements in any period...

• A
  Increases one by one from $I \, A$ to $VII \, A$.
• B
  Decreases one by one from $I \, A$ to $VIII \, A$.
• C
  Increases one by one from $I \, A$ to $IV \, A$ and then decreases one by one from $V \, A$ to $VII \, A$.
• D
  Decreases one by one from $I \, A$ to $IV \, A$ and then increases one by one from $V \, A$ to $VII \, A$.