By mass, the interstellar medium in our region of the Milky Way consists of A 50% Hydrogen, 50% Helium. B 70% Hydrogen, 30% Helium. C 70% Hydrogen, 20% Helium, 10% heavier elements. D 50% Hydrogen, 30% Helium, 20% heavier elements. E 70% Hydrogen, 28% Helium, 2% heavier elements.

13) Consider a sample of iodinc $-131$ a. How many half-lives would it take for the sample to decay until less than $1\% $ of the original isotope remained?

Identify the true statements about wavelengths of light. Select the TWO answers that are correct. Green light has more energy than any other wavelength of visible light. Red light has a longer wavelength and less energy than blue light. Plants reflect wavelengths of light that our eyes cannot detect. In the absence of visible light,photosynthesis proceeds with infrared wavelengths. Plants absorb wavelengths of light that our eyes perceive as green.

What is the change in energy of a hydrogen atom when it undergoes an electronic transition from $n_{initial}=5$ to $n_{final}=2$ $2.09\times 10^{-18}J$ $4.90\times 10^{-20}J$ $4.57\times 10^{-19}J$ $1.55\times 10^{-20}J$ $1.55\times 10^{-19}J$

When an X-ray beam with a wavelength of 120 pm strikes the surface of a crystal with a lattice spacing of 165 nm, what is the maximum reflection angle with a value of $n=1$ $32.6^{\circ }$ $54.0^{\circ }$ $21.3^{\circ }$ $38.3^{\circ }$ $18.4^{\circ }$

When we see a crescent moon the rest of the face that we see is not completely dark because __ A) it is partially facing toward the Sun B) it is slightly illuminated by sunlight reflected by Earth C) it is slightly illuminated by the light of Earth's cities D) it is slightly illuminated by starlight

What is the SI unit in the measurement of radioactivity? Multiple Choice Ci mCi uCi Bq rutherford

At what distance does the typical runner achieve maximum velocity? 15 to 20 meters 20 to 30 meters 25 miles per hour 12 meters

The same side of the moon always faces earth. True False

The larger the sample of a given substance the more dense it is. Otrue Ofalse

A mover is applying a force on a crate up an incline.The incline is slightly rough with a coefficient of kinetic friction of 0.150 If the piano is not accelerating, that is moving up the incline with constant speed, what is the magnitude of the work done by the mover if the incline is 3.00 m long and the piano has a mass of 180 kg. The angle of the incline is $10.0^{\circ }$ Use three significant digits please. $\square $ disappointed