By months of age the fetus swallows and urinates, arms and hands develop, and fingers develop nails

3 months

Explanation:

Fertilization may be defined as the process of formation of zygote by the fusion of male gamete (sperm) and female gamete (ova). Zygote divides by mitosis and remains in the human female womb for nine months.

The formation of organ development starts at the end of gastrulation process.   At the end of three months or first trimester, the fetus can urinates, swallow. The hands and arms development of fetus occurs and nails also develop on fingers.

Thus, the answer is 3 months.

a covalent bond, specfically triple bond