In the first fit, block requests will be satisfied from the first free block that fits it.
- The request for $300$ will be satisfied by a $350$ size block reducing the free size to $50$.
- Request for $25$, satisfied by $150$ size block, reducing it to $125.$
- Request for $125$ satisfied by $125$ size block.
- And request for $50$ satisfied by the $50$ size block.
So, all requests can be satisfied.
In the best fit strategy, a block request is satisfied by the smallest block that can fit it.
- The request for $300$ will be satisfied by a $350$ size block reducing the free size to $50$.
- Request for $25$, satisfied by $50$ size block as its the smallest size that fits $25$, reducing it to $25$.
- Request for $125$, satisfied by $150$ size block, reducing it to $25$.
Now, the request for $50$ cannot be satisfied as the two $25$ size blocks are not contiguous.
So, answer (B).