Which of the following combinations of reactants will result in a synthesis reaction?

cl2 + baf2
mg + hclo3
li + h2o
so2 + h2o

The first reaction from the scale Cl2 + BaF2 is decomposition, remember! that H20 should be broken down.
The third one is  metal ion substitution
The last one is decomposition again.
The second one is H2 + Cl2  has been combined in order to synthesize  2HCl, so that's the answer.

Correct Option D i.e. SO2 + H2O

Reason: 
A synthesis reaction occurs when two or more reactants combine to form a single product. This reaction can be represented as A + B → AB.
In the present case, SO2 + H2O → H2SO3

Hence, it is an example of synthesis reaction. 

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

Mg-26 and mg-24 are pair of isotopes. isotopes are defined as atoms of the same element having same atomic number but different mass number. i hope that was .