The nucleus of some isotopes, such as radium-226 shown above, will spontaneously undergo nuclear decay. These isotopes are said to be radioactive.

What causes the nucleus of an isotope to be radioactive?
A. an unstable ratio of protons and neutrons
B. the attraction of protons to electrons
C. exposure to toxic chemicals
D. too many electrons in its orbitals

Organelles are 1. responsible for producing power for the cell 2. tiny structures in the cell that carry out the cell's activities 3. responsible for digestion in the cell 4. found outside of the membrane

Acarpenter builds an exterior house wall with a layer of wood 2.9 cm thick on the outside and a layer of styrofoam insulation 2.3 cm thick on the inside wall surface. the wood has k=0.080w/(m⋅k), and the styrofoam has k= 0.010 w/(m⋅k). the interior surface temperature is 19.0 ∘c , and the exterior surface temperature is -15.0 ∘c . a.)what is the temperature at the plane where the wood meets the styrofoam? celsius b.)what is the rate of heat flow per square meter through this wall? /m^2

Decreased sensitivity to an unchanging stimulus is known as