Enter the chemical formula of a binary molecular compound of hydrogen and a group 6a element that can reasonably be expected to be less acidic in aqueous solution than h2se, e. g. have a smaller ka .

Any binary molecular compound of hydrogen and a Group 6A element above Selenium will be less acidic, so water and dihydrogen sulfide are less acidic in aqueous solution than hydrogen selenide.

Explanation:

Going down in a group increases the atomic radius and a greater atomic radius implyes greater ionic radius.  

When ionization takes place in these compounds they yelds protons (hidrogen ion) and an lewis base (anion). The greater the ionic radius the greater its stability, thus the periodic tendency is increaing the acidity of binary hidrogen compounds when going down a group. On the other hand going up a group decreases acidity, so any molecular compound of hydrogen and a Group 6A element above Selenium will be less acidic, so water and dihydrogen sulfide are less acidic in aqueous solution than hydrogen selenide.

the correct answer is:

a. formation of precipitation