Which of the following properties generally decreases along a period?

Options

A. ionisaiton energy
B. electron affinity
C. metallic character
D. valency

Answer

To determine which property generally decreases along a period in the periodic table, we can analyze the trends of various properties as we move from left to right across a period. Here’s a step-by-step breakdown:

### Step 1: Identify the properties to analyze
We need to consider several properties that may change as we move across a period. Common properties include:
- Atomic size (radius)
- Ionization energy
- Electron affinity
- Electronegativity
- Metallic character

### Step 2: Analyze atomic size
As we move from left to right across a period, the atomic size generally decreases. This is due to the increase in the effective nuclear charge (Z-effective), which pulls the electrons closer to the nucleus.

**Hint:** Remember that atomic size decreases because of increased nuclear charge attracting electrons more strongly.

### Step 3: Analyze ionization energy
Ionization energy is the energy required to remove an electron from an atom. As we move across a period, ionization energy generally increases because the atomic size decreases, and the electrons are held more tightly by the nucleus.

**Hint:** Ionization energy increases as atomic size decreases due to stronger attraction between the nucleus and electrons.

### Step 4: Analyze electron affinity
Electron affinity is the energy change when an electron is added to a neutral atom. Generally, electron affinity increases across a period, as the effective nuclear charge increases, making it easier for the atom to attract additional electrons.

**Hint:** Electron affinity increases as the atomic size decreases and effective nuclear charge increases.

### Step 5: Analyze electronegativity
Electronegativity is the tendency of an atom to attract electrons in a bond. This property also increases across a period due to the same reasons mentioned above: decreasing atomic size and increasing effective nuclear charge.

**Hint:** Electronegativity increases as atoms become smaller and more positively charged.

### Step 6: Analyze metallic character
Metallic character refers to the tendency of an element to lose electrons and form cations. As we move across a period from left to right, metallic character generally decreases. This is because elements on the left are more likely to lose electrons compared to those on the right, which tend to gain electrons.

**Hint:** Metallic character decreases because elements on the right side of the periodic table are less likely to lose electrons.

### Conclusion
From the analysis, we can conclude that the property that generally decreases along a period is **metallic character**.

### Final Answer
**Metallic character decreases along a period.**