Which statement describes a chemical property of water! Under the proper conditions, water will break apart into hydrogen and oxygen gas.
Water will dissolve sodium chloride, or table salt.
Water forms beads on a waxy surface.
The melting point of water is 0°C.

Explanation:

1 ) Under the proper conditions, water will break apart into hydrogen and oxygen gas.

When water is converted into hydrogen and oxygen , this change is irreversible under ordinary condition . It can not be possible by easy means to obtain water again from hydrogen and oxygen . Hence this is chemical change .

2 )

Water will dissolve sodium chloride, or table salt.

When sodium chloride or table salt is dissolved in water , we can easily get back salt by boiling the water off . The residue will be salt . Hence is is reversible change . Hence this represents physical change.

3 )

Formation of bead on waxy surface is not something in which any change is taking place . Bead too is a water . So it is a physical change .

4 )

When ice melts to form water , it is physical change because , we can get back ice from water easily by  putting water in freeze. Hence it is a physical change.

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.