When concentrated H2S04 (sulfuric acid) spills on a surface, it is important to clean it up immediately to prevent any damage or accidents.

Option 1 suggests cleaning it with a piece of cloth. While a cloth may help absorb some of the acid, it is not the best option as it can easily become saturated and potentially spread the acid to other areas. It is also not effective in neutralizing the acid.

Option 2 suggests adding cold water. This is not the recommended method because adding water to concentrated sulfuric acid can cause a violent reaction, resulting in the release of heat and potentially splattering the acid. This can cause harm to whoever is attempting to clean it up.

Option 4 suggests adding solid BaCl2 (barium chloride). This is also not an appropriate method to clean up sulfuric acid spills, as it does not neutralize the acid but rather forms a precipitate with it.

Option 3 is the correct answer. Adding solid Na2CO3 (sodium carbonate) is the ideal method to clean up sulfuric acid spills. Sodium carbonate is a base that can neutralize the acid, forming carbon dioxide gas and water. This reaction helps to eliminate the hazard and make the clean-up process safer.