A. Because it is using Database.Update() method so dml error will not be thrown.

list<case> cl = new list<case> ();

for (case c:[select id,status from case limit 50000]){

c.status='working';
cl.add(c);
}
try{
database.update(cl,false);
}
catch(exception e){
system.debug(e.getmessage());
}


You will get the following error

System.LimitException: Too many DML rows: 10001

B is the Correct Answer

B is correct, The keyword is "OVER"
limits of SOQL 50000 (is OK in the code)
limits of DML statements 10000 (is NOT ok because the environment that has OVER 10,000 Case records)

option B is correct
its > 10,000 not 10,000 so will exceed DML limits
https://developer.salesforce.com/docs/atlas.en-us.salesforce_app_limits_cheatsheet.meta/salesforce_app_limits_cheatsheet/salesforce_app_limits_platform_apexgov.htm
Total number of records processed as a result of DML statements, Approval.process, or database.emptyRecycleBin 10,000 10,000

Option B is correct. I tried it in my org and it gives me error Too many DML rows.

I think it's option A.
A. The transaction will succeed and changes will be committed.
Because this is bulkify code and no one exception will occur.

I got following error message.
System.DmlException: Insert failed. Suggest me which is the correct answer.

Its Option A.
Which Governor limit is exceeding??
It has only 10000 records which is permissible limit.
And Using List to call DML(Which is called only once)