In pBR322, a commonly used plasmid in genetic engineering, certain restriction sites are present within the antibiotic resistance genes, which provide resistance to tetracycline and ampicillin. Here's what would happen if foreign DNA is inserted at each of the following restriction sites:

Option A : Pst I - The PstI site is present in the ampR gene (ampicillin resistance gene). Insertion of DNA here would disrupt the ampicillin resistance gene, causing a loss of ampicillin resistance, but it would not affect tetracycline resistance.

Option B : Pvu I - Similar to PstI, the PvuI site is also present in the ampR gene. Therefore, insertion of DNA here would cause a loss of ampicillin resistance, but it wouldn't affect the plasmid's tetracycline resistance.

Option C : EcoR I - The EcoRI site is not present within either the ampR or tetR genes in pBR322. Inserting DNA at this site would not disrupt either the ampicillin or tetracycline resistance genes.

Option D : BamH I - The BamH I site is within the tetR gene. If foreign DNA is inserted at this site, it would disrupt the tetracycline resistance gene, causing a loss of tetracycline resistance.

So, the correct answer to the question "Ligation of foreign DNA at which of the following site will result in loss of tetracycline resistance of pBR322?" is Option D : BamH I.