A single member of a RAID 5 array will consist of plain blocks and parity blocks, for example 75% plain and 25% parity for a 4 member array. The plain blocks can be read in plain view; there is no scrambling of these blocks and you do not need to refer to other members to make sense of it. These blocks are typically 16KB to 512KB in size though with RAID-5 this is usually 128KB or below to minimise write amplification. There is plenty of scope to read sensitive data that appears in such plain blocks.
Each parity block contains data that is generated from three plain blocks on other drives, in such a way that if any of those three other drives (in a four-member array) is lost the information can be recovered by applying an algorithm to the parity block and the blocks from the other remaining two drives. The data in a parity block makes no sense and could not be recovered on its own, unless you could guess the content of two of the three other blocks it combines with - which may in some cases be easy if at least two of the three blocks were empty (zeroes) or contain predictable data. Thus while it's not cryptographically secure, the ability to extract data from a parity block on its own is unlikely to reveal anything useful except for in specific cases.
RAID 4 had a similar design to RAID 5 except that all the parity blocks were stored on one drive, so if you only had that drive, you would have no easily recoverable data. RAID 5 modified this to distribute the parity blocks evenly between members, meaning that any drive on its own will contain a lot of plain blocks from which you might recover data.
It's important to know that security of data is not a design goal in RAID and if you need it, you should implement it on another level.