Un elemento posee dos isótopos cuyos números de masa suman 68 y la semisuma de sus neutrones es 19. Determine el grupo de este elemento en la Tabla Periódica Actual.

The element belongs to group 15 of the present periodic table

Explanation:

Isotopes have the same proton number, what differs is that they have different number of neutrons.

Now since the half-sum of their neutrons is 19, the total number of neutrons would be 19 * 2 = 38 neutrons.

Also, their masses add up to be 68, since the total mass equals sum of neutrons and sum of protons, this means that the total number of protons is 68-38 = 30

Since this is equal in both isotopes, this means that the proton number of the element is 30/2 = 15

The atomic number is the number of protons in the nucleus of an atom. Since the atomic number is 15, this element is phosphorus and it belongs to group 15 of the present periodic table

The compound in which the atom has unfilled valence shell of electron is

Explanation:

Valence electrons is defined as the electrons which are present in the outermost shell of an atom.

Lewis-dot structure is defined as the structure which represents the number of valence electrons around the atom. The dots represents the electrons.

For the given options:

In the given compound, 2 electrons are shared between oxygen and each hydrogen atom. From the lewis dot structure,

Valence electrons in each hydrogen atom = 2

Valence electrons in oxygen atom = 8

The valence shell of both the elements is complete.

In the given compound, 4 electrons are shared between carbon and each oxygen atom. From the lewis dot structure,

Valence electrons in each oxygen atom = 8

Valence electrons in carbon atom = 8

The valence shell of both the elements is complete.

In the given compound, 2 electrons are shared between carbon and each hydrogen atom. From the lewis dot structure,

Valence electrons in each hydrogen atom = 2

Valence electrons in carbon atom = 8

The valence shell of both the elements is complete.

In the given compound, 2 electrons are shared between boron and each chlorine atom. From the lewis dot structure,

Valence electrons in each chlorine atom = 8

Valence electrons in boron atom = 6

The valence shell of boron is not complete and has incomplete octet.

Hence, the compound in which the atom has unfilled valence shell of electron is