An element consists of two isotopes. one with a mass of 79.95 amu and an abundance of 29.9%. the second isotope has a mass of 81.95 amu with an abundance of 70.1%. what is the molar mass of this element?

 the molar  mass of the element  is  81.36 g/mol

calculation

step 1 : multiply  each %abundance  of the isotope  by   its mass  number

that is 79.95 x 29.9 =2391

           81.95 x 70.1  = 5745

Step 2: add them together

2390.5 + 5744.7 =8136

Step 3: divide by 100

= 8136/100 = 81.36  g/mol

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.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.