Water is the only substance that is as a solid than as a liquid. thus it is unique in its physical properties.

Water is the only substance that is lighter as a solid than as a liquid. Thus, it is unique in its physical properties.

Explanation:

A property that does not bring any change in chemical composition of a substance are known as physical properties.

For example, shape, size, mass, volume, density, etc of a substance are all physical properties.

On the other hand, a property that changes chemical composition of a substance is known as chemical property.

For example, precipitation, reactivity, toxicity etc are chemical property.

In solid state, water has cage like structure due to which there is space present within its molecules. As a result, it becomes lighter in nature.

Hence, water is the only substance that is lighter as a solid than as a liquid. Thus, it is unique in its physical properties.

- 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

a) the particles of the chair are strongly held together.