Basic radar service to VFR aircraft includes

Referring to the airspace symbols on a VFR sectional chart, the area defined by a solid magenta border surrounding an inner dashed blue circle provides what type of radar assistance to participating VFR aircraft?

Your altimeter is set to 30.12 inHg and indicates 5,500 feet. What pressure altitude will your Mode C transponder report to ATC?

You are receiving VFR radar advisory services in Class E airspace above 10,000 feet MSL. ATC provides a traffic advisory, but shortly after, they inform you they have lost your Mode C target on their display. You check and realize you inadvertently selected the 'ON' position instead of 'ALT' on your transponder. What is the most effective immediate action to mitigate the risk of reduced situational awareness?