What is the expiation for backbiting, gossip, and ridiculing religious scholars, rulers, singers, disbelievers, and the deceased? Is it obligatory to apologize to them despite the difficulty of reaching them?

A Muslim must repent to Allah Almighty from mockery and backbiting, which are blights of the tongue forbidden by the Qur’an and Sunnah. Every word a person utters is recorded against him, and the true Muslim is he from whose tongue and hand other Muslims are safe. Mocking people and backbiting them distances a Muslim from his Lord and leads him to Hellfire. Scholars have warned against slandering people, especially scholars, because "the flesh of scholars is poisoned." If a Muslim falls into backbiting and mockery, he must regret it and repent. If it is possible to seek forgiveness from those wronged without causing further mischief, then he should do so. Otherwise, it is sufficient to seek forgiveness for them and mention them with goodness in the situations where he backbiting them. This is the view of some scholars, such as Ibn Taymiyyah and Ibn al-Qayyim. And whoever repents, Allah will accept his repentance.