An atom with atomic number 20 is most likely to combine chemically with the atom whose atomic number is

Options

A. 3
B. 11
C. 17
D. 18

Answer

To solve the question, we need to determine which atom an atom with atomic number 20 (calcium) is most likely to combine with chemically. Here’s a step-by-step solution:

### Step 1: Identify the Element with Atomic Number 20
The element with atomic number 20 is calcium (Ca). Calcium is a metal and is located in Group 2 of the periodic table.

**Hint:** Look up the periodic table to find the element corresponding to the atomic number.

### Step 2: Determine the Chemical Behavior of Calcium
Calcium, being a metal, tends to lose electrons and form cations with a +2 charge (Ca²⁺). Metals typically react with non-metals to form ionic compounds.

**Hint:** Remember that metals usually lose electrons, while non-metals tend to gain electrons.

### Step 3: Identify Possible Reactants
We need to consider which atoms can combine with calcium. The options provided in the question include various elements. We will check the atomic numbers of these elements to see if they are metals or non-metals.

**Hint:** List the atomic numbers of the elements you are considering for potential reactions with calcium.

### Step 4: Analyze the Options
1. **Atomic Number 1 (Hydrogen, H)**: Hydrogen is a non-metal and can react with calcium to form calcium hydride (CaH₂).
2. **Atomic Number 11 (Sodium, Na)**: Sodium is also a metal and would not react with calcium.
3. **Atomic Number 17 (Chlorine, Cl)**: Chlorine is a non-metal and can react with calcium to form calcium chloride (CaCl₂).

**Hint:** Identify which of the elements are non-metals, as these are the ones that will likely react with calcium.

### Step 5: Determine the Best Option
Among the options, chlorine (atomic number 17) is a non-metal that can react with calcium to form an ionic compound (CaCl₂). While hydrogen can also react, the question asks for the most likely combination, and typically, non-metals like chlorine are more common reactants with metals like calcium.

**Hint:** Consider the stability and commonality of the compounds formed when determining the best answer.

### Conclusion
The atom with atomic number 20 (calcium) is most likely to combine chemically with the atom whose atomic number is **17 (Chlorine)**.

**Final Answer:** Atomic number 17 (Chlorine) is the correct answer.