Which condition favors shielding of hydrophobic bases in low stringency?

High salt conditions favor the shielding of hydrophobic bases during low stringency because the presence of salts can stabilize the interactions between nucleic acids. When high salt concentrations are present, these ions help to shield the negative charges on the phosphate backbone of DNA or RNA. This shielding allows for a greater degree of association between complementary strands, which means they can hybridize despite having mismatches.

Low stringency is characterized by conditions that permit less specific binding between nucleic acids, often leading to the formation of hybrid strands that might contain mismatched bases. Under these circumstances, high salt acts to reduce the repulsion between the negatively charged phosphates, helping maintain structural integrity around the bases and allowing for a more permissive hybridization environment.

In contrast, high temperature would disrupt hydrogen bonding and destabilize nucleic acid structures, while low formamide concentrations would not provide the same level of ionic shielding that high salt does. Low temperature, although it may reduce kinetic energy and allow for some hybridization, does not specifically enhance the shielding effect as effectively as high salt does. Thus, the correct choice highlights the specific role of high salt in stabilizing hydrophobic interactions during low stringency conditions.