Final answer:
The argument between Bruno's father and grandmother arises due to the father's role in the Nazi concentration camp, which the grandmother condemns. This heavily conflicting issue fuels continuous disagreements between them.
Step-by-step explanation:
The most likely cause of the argument between Bruno's father and grandmother in the novel The Boy in the Striped Pajamas by John Boyne is Bruno's father's role as a commandant in a Nazi concentration camp. The grandmother disapproves of her son's involvement with the Nazi party, leading to intense conflict and disagreement.
The grandmother expresses strong negative feelings about the Nazi party, their ideology, and the actions they are taking against innocent people. This deeply held belief pits her against her son, who has chosen to follow orders and partake in heinous crimes against humanity. Such a contentious topic would surely lead to arguments and strain in their relationship, making it a plausible cause for the tension and fights witnessed by Bruno.
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