Quick Answer. Cardiopulmonary resuscitation, or CPR, courses are two to five hours long and the certification lasts for two years, states American Red Cross. CPR is an emergency technique used to attempt to save a personâs life if he has stopped breathing or if his heart has stopped beating, says Mayo Clinic. Continue Reading.
This feature is not available right now. Please try again later. In 1950, Zenith introduced the Cobra-Matic variable speed automatic record changer -- the first and only changer that plays any speed record now made or yet to come, 10 rpm to 85...with two simple controls a six-year-old can operate..
Benzene is the simplest aromatic compound with C6H6 molecular formula and contains three pi bonds arranged in alternate manner in hexagonal ring. The carbon-carbon bond length in benzene is intermediate to C-C single bond (154 pm) and C = C double bond (134 pm) that is 139 pm due to resonance in molecule.ince six pi electrons are delocalized over whole ring, therefore the cyclically conjugated double bonds represents by a circle and the carbon-carbon bond length becomes equal. This structure of benzene is called as resonance hybrid of benzene and generally used to represents the benzenemolecule.