Element x had a mass of 300g and a 1/2 life of 10 years. how many grams will remain after 40 years?

18.75 grams

Remaining mass = Original mass × (1/2)^n, where n is the number of half-lives

Number of half-lives = Time for the decay ÷ Half-life

                                 = 40 years ÷ 10 years

                                  = 4

Therefore;

Remaining mass = 300 g × (1/2)⁴

                            = 300 g × 1/16

                             = 18.75 g

Hence, a mass of 300 g of an element X decays to 18.75 g after 40 years.

asking the goog might u get an answer

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.