Which of the following chemical equations is NOT correctly balanced?

• A. C_3H_8 + 5 O_2 → 3 CO_2 + 4 H_2O
• B. 2 H_2 + O_2 → 2 H_2O
• C. Na + Cl_2 → 2 NaCl
• D. 2 KClO_3 → 2 KCl + 3 O_2

Answer: (C)

Verified step by step guidance

1. Step 1: Understand that a balanced chemical equation has the same number of atoms of each element on both sides of the reaction arrow.
2. Step 2: Check the first equation: \(C_3H_8 + 5 O_2 \rightarrow 3 CO_2 + 4 H_2O\). Count atoms on both sides: Carbon (C): 3 on left and 3 on right; Hydrogen (H): 8 on left and 4×2=8 on right; Oxygen (O): 5×2=10 on left and (3×2)+(4×1)=6+4=10 on right. This equation is balanced.
3. Step 3: Check the second equation: \$2 H_2 + O_2 \rightarrow 2 H_2O$. Count atoms: Hydrogen (H): 2×2=4 on left and 2×2=4 on right; Oxygen (O): 2 on left and 2×1=2 on right. This equation is balanced.
4. Step 4: Check the third equation: \(Na + Cl_2 \rightarrow 2 NaCl\). Count atoms: Sodium (Na): 1 on left and 2 on right; Chlorine (Cl): 2 on left and 2 on right. Sodium atoms are not balanced, so this equation is NOT balanced.
5. Step 5: Check the fourth equation: \$2 KClO_3 \rightarrow 2 KCl + 3 O_2$. Count atoms: Potassium (K): 2 on left and 2 on right; Chlorine (Cl): 2 on left and 2 on right; Oxygen (O): 2×3=6 on left and 3×2=6 on right. This equation is balanced.