Singly ionized helium is a hydrogen-like atom that has a nuclear charge of Its energy levels are given by where and If a beam of visible white light is sent through a gas of singly ionized helium, at what wavelengths will dark lines be found in the spectrum of the transmitted radiation?

28. evolution

29. environment, survive, offspring  

explanation:

myth. it was once thought that animals, including cats and dogs, could only see in black and white. however, scientists have proven this to be a myth. in all animals, including humans, the perception of colour is determined by the presence of cells in the eye called cone photoreceptors.

prndulum needs thread, weight clock to time swings