Which among the following cause the variation ?

All of these .

The correct answer is Option (4) → All of these .

All of the options mentioned—sexual reproduction, cross-pollination, and xenogamy—can contribute to genetic variation within a population.

Sexual reproduction, involves the fusion of gametes from two parent organisms, leading to offspring with unique combinations of genes and promoting genetic diversity.

Cross-pollination, brings genetically diverse pollen from one plant to another, increasing the genetic variation within the population. This genetic diversity is advantageous for the population's overall fitness and adaptability to changing environmental conditions. By preventing self-pollination and promoting outcrossing, self-incompatibility helps maintain genetic diversity within a population, reducing the risk of inbreeding depression.

Xenogamy: Transfer of pollen grains from anther to the stigma of a different plant .This is the only type of pollination which during pollination brings genetically different types of pollen grains to the stigma.

Therefore, all three processes—sexual reproduction, cross-pollination, and xenogamy—can contribute to genetic variation in different ways and to different extents.