The existence of a substance in more than one solid modification is known as:

$A$ sodium atom is in one of the states labeled 'Lowest excited levels'. It remains in that state for an average time of $10^{-8} \ s$,before it makes a transition back to a ground state. What is the uncertainty in energy of that excited state?

$A$ neutrino is a particle,which is

During transcription,the site on $DNA$ where $RNA$ polymerase binds is called .........

Identify the correct decreasing order of the following with respect to altitude from the atmosphere:
$I$. Troposphere
$II$. Mesosphere
$III$. Thermosphere

Assertion : $Pb^{4+}$ compounds are stronger oxidizing agents than $Sn^{4+}$ compounds.
Reason : The higher oxidation states for the group $14$ elements are more stable for the heavier members of the group due to 'inert pair effect'.