Inserting The Missing Character Questions

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

P_QR_QQ_PQ_R

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

W_YZ_X_ZW_Y_

Select the missing numbers from the given alternatives

Which set of letters when sequentially placed at the gaps in the given letter series shall complete it?

j_l_jk_m_kl_

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

Select the missing number?

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

A, D, I, P, ?

Which set of letters when sequentially placed at the gaps in the given letter series shall complete it?

A_BC_BBC_BB_