Which elements can react to produce a molecular compound?
(1) calcium and chlorine
(2) hydrogen and sulfur
(3) lithium and fluorine
(4) magnesium and oxygen

 The  elements that can react  to produce a molecular  compound is  hydrogen  and sulfur

Explanation

A  molecular compound is   formed  when two or more atoms join by  sharing  electrons through  a  covalent  bond.   Sharing of atoms  occurs  mainly  between non metals.
Hydrogen ( a non metal)  and sulfur(a non metal) react to form  a molecular compound  by sharing electron among themselves.2 hydrogen  atom   bond  with 1 atom sulfur  to form hydrogen sulfide.

the catch is that the top numbers are atomic masses the bottom numbers are the numbers of protons and electrons in an uncharged atom. they are the number of that atoms as you would find them on the periodic table. further, the numbers on the left are used to determine the missing numbers on the right

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts