Can you claim the royal throne if you kill the king/queen?

If you had an entire army, and took over the country in a coup de etait, yes. Otherwise, no. Being a King/Queen is not a survival game!

You must be related to a royal to have a claim to the throne. It can be a very distant relation indeed - the British monarchs were still claiming the French throne until 1800, despite George III being an INCREDIBLY distant relative of the original claimant, Edward III (himself the nephew of Charles IV, the last of the Capetian kings of France). George was a grandson of George I, himself a distant cousin of the previous monarch Anne. She was a great niece of Elizabeth, who was the grand daughter of Henry VII - who only had a very tenuous claim to the throne - he was descended illegitimately from John of Gaunt, the 3rd son of Edward III. If you are no relative at all then you have no claim.

Of course, way back in history it was simply down to whoever had the biggest army. Burgundy was taken by the French because Charles the Bold of Burgundy was killed in a battle and the French simply invaded. It wasn't whoever killed him (probably a peasant, as his head was cleft by a halberd, a commoner's weapon) that got to claim his lands but the King of France, the person with the largest army.

You can.

Then again you can claim it without killing anybody.

Killing the current throne owner just slightly increases your chance off actually getting what you claim.

Not in this day and age. Centuries and centuries ago, this was how kingdoms were formed--through take overs by war lords. Today, this act would get a person arrested and tried for treason.

Depends which country. You wouldn't get away with it in the UK, and even assuming you overcome the matter of regicide, you would have to be a descendant of the Electress of Hanover to have any real claim.

You can claim it, but you wont get it. You'll be placed in a prison cell and it will be very difficult for you to access it. Killing the monarch is considered treason. Treason is a crime.

No, there would be other close relatives of the slain to take their place.

Yes if you're related

no. that would be murder. you would go to prison.