The murder of the king is called-

• The murder of the king is called- ঘ) Regicide

• Regicide (Noun)
- English Meaning: The murder of the king; the killing of a king.
- Bangla Meaning: রাজহত্যা।

• Other options:
ক) Sororicide (ভগ্নী হত্যা): The act of killing one's sister.

খ) Homicide (নরহত্যা): A killing of one human being by another.

গ) Parricide (পিতৃ-মাতৃ হত্যা; স্বজনহত্যা): One that murders his or her father, mother, or a close relative.

Source:
1. Accessible Dictionary by Bangla Academy.
2. Merriam-Webster Dictionary.