The students of class IX have made placards showing the symbols of some elements and valencies of these elements. These placards somehow got mixed up as shown below :

On this basis of these placards the chemistry teacher, Mrs. Shanti, asked a student Vikas to answer the following questions :
(a) Choose the symbol of an element from among the placards which exhibits valencies of 3 and 5. What is the name of is the name of this element ? Is it a metal or a non-metal ?
(b) Choose the symbol of an element from the given placards which shows a valency of 2. What is the name of this element ? Is it a metal or a non-metal ?
(c) Work out the formula of the compound formed between the element of valency 3 and element of valency 2. Also name this compound
(d) What values are displayed by Vikas in this episode ?