Question

how many neutrons are in phosphorus? *
20
16
13
15

how many electrons are in a neutral element of calcium? *
20
19
21
22

what characteristic is shared by elements in groups 3-12 (transition metals)?
they have 8 valence electrons
they are all gases
they are poor conductors of electricity
they are less reactive than alkali metals

Explanation:

First Question: How many neutrons are in Phosphorus?

Step1: Recall the formula for neutrons

The number of neutrons in an atom is calculated by the formula: $ \text{Number of neutrons} = \text{Atomic mass} - \text{Atomic number} $

Step2: Find atomic mass and number of Phosphorus

Phosphorus has an atomic number of 15 (number of protons) and an atomic mass of approximately 31 (the most common isotope).

Step3: Calculate the number of neutrons

Using the formula: $ 31 - 15 = 16 $

Step1: Recall the rule for neutral atoms

In a neutral atom, the number of electrons is equal to the number of protons (atomic number).

Step2: Find the atomic number of Calcium

Calcium has an atomic number of 20.

Step3: Determine the number of electrons

Since it's neutral, the number of electrons is equal to the atomic number, so 20.

• Option 1: Elements with 8 valence electrons are noble gases (Group 18), not transition metals. Eliminate.
• Option 2: Transition metals are typically solids (except mercury), not all gases. Eliminate.
• Option 3: Transition metals are good conductors of electricity (due to delocalized electrons). Eliminate.
• Option 4: Alkali metals (Group 1) are highly reactive. Transition metals are less reactive than them. This is correct.

Answer:

16 (corresponding to the option "16")

Second Question: How many electrons are in a neutral element of Calcium?