When a packet passes through a Network Address Translation (NAT) device from an internal network to an external network, the NAT device modifies the following fields in the IP header: Source IP: The NAT device replaces the source IP address in the IP header with its own external IP address. This allows devices on the external network to send responses back to the NAT device, which can then forward them to the appropriate internal device. Header Checksum: The header checksum is typically recalculated by the NAT device to ensure that it reflects any changes made to the IP header, such as the modification of the source IP address.

Option C (TTL) is decremented by each visited router. When it reaches to Zero, then Packet will be discarded.
Option A (Checksum) needs to be updated by each visited Router since TTL Value is modified.
Option D (Length) also modified whenever there is a need of performing the fragmentation process.
Option B (Source Address) can’t be modified by an IP router. Only NAT can modify it.

A record route option is used to record the internet router that handles the datagram. It can be used for debugging and management purpose.
In IPv4 header, 40 bytes are reserved for OPTIONS.
For Record Route to stores, 1 byte is used to store type of option, 1 byte for length and 1 byte for pointer. Out of 40 bytes, 37 bytes are left.
Each IP4 address takes 32 bits or 4 bytes.
Therefore, it can store at most floor (37/4) = 9 router addresses.
Hence correct answer is 9 router address.