For Contiguous allocation we can access any blocks directly( like as in array we can access any element directly), So to access block 4 while we are at 10.. we can directly access it.. which would require only 1 block access.
For Linked allocation, Direct access is not possible. As all blocks linked together and contain address of next block like as linked list. So to access any block, we have to start from the first block.. so it would require 4 block access.
For indexed allocation, Direct access is also possible, But first,we have to know the indexing of that block through index block. So to access a block first we have to access the index block to know its address and then can directly access that block. So 2 block access would be required here.