What is the rate constant of a first-order reaction that takes 143 seconds for the reactant concentration to drop to half of its initial value?

k = 4.85 x 10⁻³ / s

Explanation:

For a first order reaction we have two very important equations we need to memorize:

ln ( N/N₀ ) = -kt

and,

0.693/ k = t₁/₂

where k is the rate constant and t i is the halflife which can be derived from the first equation.

0.693/ k = t₁/₂   ⇒  k = 0.693 / t₁/₂  

k = 0.693 / 143 s = 4.85 x 10⁻³ / s

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.

i think that the answer is c