The letters in the series are alternative and the numbers indicate their position in the English alphabet from the beginning.

A + 3 = D + 4 = H + 5 = M + 6 = S + 7 = Z

Z - 5 = U - 4 = Q - 3 = N - 2 = L

Numbers : 2 + 2 = 4 + 4 = 8 + 6 = 14 + 8 = 22
Letters : B + 1 = C + 2 = E + 3 = H + 4 = L

The given sequence is a combination of two series:
I: M, O, R, V and
II: N, L, I, ?
The pattern in I is: M + 2 = O + 3 = R + 4 = V
The pattern in II is : N - 2 = L - 3 = I - 4 = E
So, the missing letter is E.

There is a gap of four letters between the first and second, the second and third letters of each term, and also between the last letter of a term and the first letter of the next term.

Y - 2 = W - 3 = T - 4 = P - 5 = K - 6 = E - 7 = X - 8 = P - 9 = G

The given sequence is a combination of two series:
I: Y, T, O and
II: B, G, ?
I: consists of 2nd, 7th and 12th letters from the end of the English alphabet, while II: consists of 2nd, 7th and 12th letters from the beginning of the English alphabet.
So, the missing letter in is the 12th letter from the beginning of the English alphabet, which is L.

1st letter :1 + 4 = 5 + 4 = 9 + 4 = 13 + 4 = 17
2nd letter :C + 3 = F + 3 = I + 3 = L + 3 = O
3rd letter :V - 1 = U - 1 = T - 1 = S - 1 = R
Thus, the term 15LS is wrong and must be replaced by 13LS.

In the first step, one letter from the beginning and one from the end of a term are removed to give the next term. In the second step, two letters from the beginning of a term are removed. These two steps are repeated alternately.

1st letter : C + 3 = F + 3 = I + 3 = L
Number : 4 (22 ) → 9 (32 ) → 16(42 ) → 25 (52 )
3rd letter : X - 3 = U - 3 = R - 3 = O

A + 8 = I + 7 = P + 6 = V + 5 = A + 4 = E + 3 = H

Each term of the series is obtained by removing two letters from the preceding term- one from the beginning and one from the end. So, the missing term is PENDICU.

One letter from the beginning and one from the end of a term are removed, one by one, in alternate setps,

a + 3 = d - 1 = c + 3 = f - 1 = e + 3 = h - 1 = g + 3 = j - 1 = i

The given series may be divided into 2 series:
I: A, B, C, D, E, F, ?, ? and
II: N, O, P, ?
Clearly , the given series consists of two terms of followed by one term of II.
The missing terms in I are G and H while the missing term in II is Q.

The given sequence is a combination of two series:
I: Z, W, T, Q, ? and
II: S, O, K, G,, ?
The pattern in I is: Z - 3 = W - 3 = T - 3 = Q - 3 = N
The pattern in II is : S - 4 = O - 4 = K - 4 = G - 4 = C

Each term consists of consecutive letters in order. The number of letters in the terms goes on increasing by one at each steps. Also, there is a gap of one letter between the last letter of the first term and the first letter of the second term; a gap of two letters between the last letter of the second term and the first letter of the third term; and so on. So, there should be a gap of three letters between the last letter of the third term and the first letter of the desired term.

The given sequence is a combination of two series:
I: C, F, I, L, O and
II: Z, X, V, T, ?
The pattern in I is :C + 3 F + 3 I + 3 L + 3 O + 3 R
The pattern in II is: Z - 2 X - 2 V - 2 T - 2 R

The given sequence is a combination of two series:
I: 1st , 3rd, 5th, 7th, 9th, 11th terms i.e., A, B, C, D, E, ?
II: 2nd, 4th, 6th, 8th, 10th terms i.e., B, D, F, H, ?
Clearly , I: consists of consecutive letters while II: consists of alternate letters.
So, the missing letter in I is F, while that in II is J.
So, the missing terms i.e., 10th and 11th terms re J and F respectively.