What signifies a dangerous level of lead on surfaces with sodium sulfide solution?

A positive reaction with a 6-8% sodium sulfide solution indicates a dangerous level of lead on surfaces because this concentration is specifically used for lead detection. When lead is present, the sodium sulfide solution reacts with it to produce a colored precipitate, typically a black or dark brown compound. This indicates that lead levels are high enough to pose a significant risk to health, thus confirming lead contamination. Monitoring lead levels accurately is crucial for ensuring safety, especially in environments where children might be exposed.

The other options do not indicate dangerous levels of lead. A negative reaction with a 1% solution would suggest that lead is not present at levels of concern, while no reaction at all implies there is no lead contamination. Additionally, a reaction only at high temperatures does not relate to standard lead testing procedures and would not be applicable to assessing lead hazard levels in typical scenarios. Understanding the specific concentrations and reactions involved in detecting lead helps ensure effective risk assessment and protective measures.