Nothing. The task is automatically displayed on the Account page.

Nothing. The Task cannot be related to an Account and a Contact.

Create a Workflow rule to relate the Task to the Contact's Account.

Create an Account formula field that displays the Task information.

Performance Tree tab under Stack Tree panel

Execution Tree tab under Stack Tree panel

Timeline tab under Execution Overview panel

Save Order tab under Execution Overview panel

Create a Sharing Rule comparing the custom object owner to the account owner.

Create a validation rule on the custom object comparing the record owners on both records.

Include the sharing related list on the custom object page layout.

Ensure that the relationship between the objects is Master-Detail.

System.debug('Amount of CPU time (in ms) used so far: ' + Limits.getCpuTime() );

List contacts = [SELECT Id, Salutation, FirstName, LastName, Email FROM Contact WHERE
AccountId = :a.Id];

If(o.accountId == a.id)

Update contactList;

In activity settings,uncheck roll-up activities to a contact's primary account

By default,tasks do not display on the account activity timeline

Use process builder to create a process to set the task account field to blank

Create a task trigger to set the account field to NULL

Use the Schema.userInfo.Opportunity.getDefaultRecordType() method.

Create the opportunity and check the opportunity.recordType before inserting, which will
have the record ID of the current user's default record type

Query the Profile where the ID equals userInfo.getProfileID() and then use the
profile.Opportunity.getDefaultRecordType() method.

Use Opportunity.SObjectType.getDescribe().getRecordTypeInfos() to get a list of record
types, and iterate trought them untilisdefaultRecordTypeMapping() is true.

Process builder

An assignment rules.

A workflow rules.

Scheduled apex.