已知：O₂(g) = O₂⁺(g)+e^- △H1= +1175.7 kJ·mol^-1

PtF₆^-(g) =PtF₆(g)+e^- △H2= +771.1 kJ·mol^-1

O₂⁺(g)+PtF₆^-(g) =O₂PtF₆(s) △H3= -482.2 kJ·mol^-1

则反应O₂(g)+PtF₆(g) = O₂PtF₆(s)的△H是 [ ]

A．77.6 kJ

B．-77.6 kJ·mol^-1

C．+77.6kJ·mol^-1

D．-886.8kJ·mol^-1

活塞环的常见故障有哪些？