Answer:
10 chromosomes
Step-by-step explanation:
Ten (10) chromosomes would be found in each cell of Arabidopsis thaliana during prophase.
The prophase stage represents the first stage of the mitotic division immediately after the interphase. A diploid cell has 2n number of chromosomes and the ploidy level of a cell remains intact throughout the interphase to the prophase stage of mitosis.
At the prophase, the chromosomes of a cell only condense and become visible under the microscope. Each chromosome is seen as being consisting of two sister chromatids joined together by a structure known as the centromere.
Hence, the number of chromosomes in the cells of Arabidopsis thaliana would remain the same even at the prophase stage of mitosis.