D,A,L and Q are 16^th group elements of Modern periodic table. The correct trend of bond angle in their hydrides is H₂D > H₂A > H₂L > H₂Q. The element ‘Q’ in the sequence is

Down the group as the size of the atom increases affinity of hydrogen towards central atom decreases. Therefore

a) X-H bond enthalpy decreases….O-H>S-H>Se-H>Te-H;

b) Thermal stability decreases….H₂O>H₂S>H₂Se>H₂Te;

H₂O and H₂S are exothermic products, remaining three hydrides are endothermic products.

c) Reducing power increases…..H₂O<H₂S<H₂Se<H₂Te;

d) Acidic strength (K_a) increases…..H₂O<H₂S<H₂Se<H₂Te;

e) p^K_a decreases…..H₂O>H₂S>H₂Se>H₂Te;

Down the group as vanderwaal's forces increases

Melting and boiling points increases

Expected BP and MP….H₂O<H₂S<H₂Se<H₂Te

Due to H-bonding in H₂O, it has higher BP and MP than expected.

BP trend…...H₂S<H₂Se<H₂Te<H₂O

MP trend….H₂S<H₂Se<H₂Te<H₂O

Central atom in these hydrides contain two lone pairs, according to Bent rules

As the Electronegativity of central atom decreases,

Bond angle decreases…..H₂O>H₂S>H₂Se>H₂Te;