Verbal Reasoning - Mental Ability Questions

In the following question, from the given alternative words, select the word which cannot be formed using the letters of the given word.
Representation

In a certain code language, '+' represents 'x', '-' represents '+', 'x' represents '÷' and '÷' represents '-'. What is the answer to the following question?
72 x 9 - 14 + 2 = ?

In the following question, which one set of letters when sequentially placed at the gaps in the given letter series shall complete it?

K_L_K_LN_M_N

A series is given with one term missing. Choose the correct alternative from the given ones that will complete the series.

DG, JM, PS, VY, ?

A series is given with one term missing. Choose the correct alternative from the given ones that will complete the series.

Hydrogen, Helium, Lithium, ?

Choose the odd word/letters/number/number pair from the given alternatives.

In the following question, which one set of letters when sequentially placed at the gaps in the given letter series shall complete it?

S_RTR_ST_T_S

In a certain code language, '÷' represents '+', '-' represents 'x', '+' represents '÷' and 'x' represents '-'. Find out the answer to the following question.

17 - 20 + 5 x 30 ÷ 4 = ?