Is this cell haploid or diploid? How can you tell?

The cell shown in the image is haploid, which can be affirmed by the presence of an odd number of chromosomes.

Explanation:

Haploid cells are those that have a single set of chromosomes, that is, half of the chromosomal charge (n) of an organism. These cells correspond to gametes.

Diploid cells are those with complete chromosomal charge (2n) and correspond to somatic cells.

The cell shown in the image is a haploid cell, since it has only three chromosomes. Because diploid cells contain chromosomes in pairs, even if the haploid cell of that species is odd or pair, diploids will always have an pair number of chromosomes.

"do a testcross with a homozygous recessive plant."