Which of the following is the measure of radio active decay rate?
alpha emission
beta emission
half-life
gamma emission

Option C

Explanation:

Radioactive decay is the loss of elementary particles from an unstable nucleus, ultimately changing the unstable element into another more stable element.

The number of protons and neutrons found in the daughter nuclei (the nuclei produced from the decay) are determined by the type of decay or emission that the original element goes through.

There are two ways to characterize the decay constant: mean-life and half-life. In both cases the unit of measurement is seconds. As indicated by the name, mean-life is the average of an element's lifetime and can be shown in terms of following expression  

Nt=N₀ * e^(−λt).

Half-life is the time period that is characterized by the time it takes for half of the substance to decay (both radioactive and non-radioactive elements).The rate of decay remains constant throughout the decay process. It is shown by:-

Nt=N₀* (1/2)^(t/t₁₂).

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.

the answer is minerals.