Does our body need energy when we are sleeping

True or false when elements combine to form a mixture, the resulting chemical properties may be very different from those of the elements that make it.

In a good thermo flask the main cause of heat loss is

The atoms in a nickel crystal vibrate as harmonic oscillators with an angular frequency of 2.3 × 1013 rad/s. the mass of a nickel atom is 9.75 × 10-26 kg. what is the difference in energy between adjacent vibrational energy levels of nickel? (h = 6.626 × 10-34 j • s, , 1 ev = 1.60 × 10-19 j)