Recall the nature of oxides

In general:

• Metal oxides are usually basic.
• Non-metal oxides are usually acidic.
• Some oxides can be amphoteric or neutral, but here we identify the given ones directly.

Classify each oxide

• $CaO$ : calcium oxide is a basic oxide because calcium is a metal.
• $SiO_2$ : silicon dioxide is an acidic oxide.
• $B_2O_3$ : boron oxide is an acidic oxide.
• $N_2O$ : nitrous oxide is a neutral oxide.
• $BaO$ : barium oxide is a basic oxide.

Check each option

A: $CaO,\ SiO_2$

• $CaO$ is basic
• $SiO_2$ is acidic
• Not both acidic

B: $B_2O_3,\ CaO$

• $B_2O_3$ is acidic
• $CaO$ is basic
• Not both acidic

C: $B_2O_3,\ SiO_2$

• $B_2O_3$ is acidic
• $SiO_2$ is acidic
• Both are acidic

D: $N_2O,\ BaO$

• $N_2O$ is neutral
• $BaO$ is basic
• Not both acidic

Final answer

The pair of acidic oxides is: $\boxed{C:\ B_2O_3,\ SiO_2}$

Comparison with stored correct answer

Stored correct answer is C, which matches the derived answer.