The Given situation can be represented as under:

Given Number :      2 5 6 7 3 9 4 8

Ascending order :  2 3 4 5 6 7 8 9

Specified letters are 6 and 4 respectively.

Hence, required sum = (4 + 6 = 10)

The given numbers are :

382  473  568  728  847  629

When changes are made as given in the question, numbers become as follows :

238  347  856  872  784  962

Again now, find out the difference between the numbers given in options as given below:

(1) 473 - 382  => 347 - 238 = 109

(2) 629 - 728  => 962 - 872 = 90

(3) 629 - 847  => 962 - 784 = 178

(4) 728 - 847  => 872 - 784 = 88

Here the given numbers are 

567  284  696  865  738

When 1 is added to the last digit of each of the above numbers, it becomes as follows :

568  285  697  866  739

After reversing the order of digits , we get

865  582  796  668  937

Now , when the numbers are arranged in ascending order their order becomes as follows:

582  668  796  865  937

Hence , the fourth number is 865 (a number formed by 567). Therefore option(1) is correct answer.

Second, fourth and the sixth digits of the number are 3, 1 and 6. Using these digits only once we can make 361, which is a perfect square number. Hence, our answer is 19 x 19 = 361

There are 10 digits. Now, third digit from the right means (10-3+1 = ) 8th digit from the left.  But, from the question , third  and eighth digits are interchanged. Hence, the required digit is the third digit of the given number, ie 0.

Given Number :  7 6 5 3 4 2 1 8 

New Number :    8 7  6 4 5 3 2 9

Ascending Order :  2 3 4 5 6 7 8 9 

Fifth digit in the above ascending order arrangement is '6' . Hence option(1) is the correct answer.

Three persons A, B, C can be arranged in a queue in six different ways, ie ABC, CBA, BAC, CAB, BCA, ACB. But since there are only 3 persons ahead of C, so C should be in front of the queue. Thus, there are only two possible arrangements, ie CBA and CAB.

We may consider the two cases as under:

Case I:  ←3C↔8B↔5A→21

Clearly, number of persons in the queue = (3+1+8+1+5+1+21=) 40

Case II:  ←3C A↔5B

Number of persons between A and C                  

= (8 - 6) = 2   

∵[C↔8B A→21B]

Clearly number of persons in the queue = (3+1+2+1+21) = 28

Now, 28 < 40. So, 28 is the minimum number of persons in the queue.