Any chemical or physical change that absorbs energy 1. cannot occur spontaneously. 2. forms products with less mass than the initial reactants. 3. is an endothermic process. 4. has high activation energy.

3. is an endothermic process.

Explanation:

Generally, reactions can be classified into two. Depending on whether they absorb heat -energy or release energy.

Endothermic Reactions are those reactions in which the reaction absorb heat form the surroundings.

Exothermic reactions are those reactions that release heat to the surroundings.

This means the correct option is;

3. is an endothermic process.

- calcium has greater affinity to bond with electron receptors than hydrogen does and hence, it has the ability to replace hydrogen in most of its compounds.

- lithium has 2 valence electrons in the product because it can make only 1 bond with hydrogen. beryllium has 4 valence electrons in the product because it can only make 2 bonds. it has fewer electrons than neon and can react with electron donors. each hydrogen has 2 valence electrons, the same as helium.

- the covalent bond formed between carbon and hydrogen is polar because carbon is more electronegative than hydrogen and it attracts the bonded electron pair closer to itself, thus giving hydrogen a partial positive charge.

- a hydrogen bond is a relatively weak bond that hydrogen atoms make with the electronegative atoms nitrogen, oxygen or fluorine.

so the best choice is a.) 2 calcium (ca) atoms