Atomic Spectra

Step 1: Understanding Dissolved Oxygen (DO) in Water
- Dissolved oxygen (DO) is essential for the survival of aquatic organisms, including fish.
- The minimum required concentration of DO for fish growth is generally 6 ppm (parts per million).
- If the DO level drops below this threshold, it can lead to stress and suffocation in fish populations.

Step 2: Verifying the Correct Answer
- The recommended minimum concentration of DO in natural water bodies for healthy fish growth is 6 ppm.
- The other options (8 ppm, 10 ppm, 12 ppm) represent higher concentrations that are beneficial but not the absolute minimum required.
- Thus, the correct answer is 6 ppm (Option 4).

Step 1: Understanding Dipole Moment A molecule has a permanent dipole moment if:
- It has polar bonds due to electronegativity differences.
- The molecule has an asymmetrical shape, leading to a net dipole moment.

Step 2: Analyzing the Given Molecules
- Nonpolar Molecules (No Dipole Moment):
- (tetrahedral, symmetrical)
- (tetrahedral, symmetrical)
- (square planar, symmetrical)
- (linear, symmetrical)
- Polar Molecules (Have Dipole Moment):
- (trigonal pyramidal, asymmetric)
- (bent, asymmetric)
- (linear, polar bond)
- (see
-saw shape, asymmetric)
- (bent, asymmetric)
- (square pyramidal, asymmetric)
- (bent, asymmetric)

Step 3: Counting Molecules with Dipole Moment Polar molecules: Total = 7 molecules. Thus, the correct answer is .

Step 1: Understanding the Structure
- The given image represents a tetrahedral carbon center with four different groups attached.
- The wedge-dash representation is used to show 3D molecular structures:
- Solid wedge (triangle) represents a group coming out of the plane (toward the viewer).
- Dashed wedge (dashed line) represents a group going behind the plane (away from the viewer).
- Straight lines represent groups in the plane of the paper.

Step 2: Identifying the Groups in the Plane of the Paper
- The two groups represented by straight lines are in the plane of the paper.
- From the given structure, the groups in the plane are CH , C H , and C.
- Therefore, the correct answer is Option (4) CH , C H , C.

Step 1: Understanding the Octet Rule The octet rule states that atoms tend to form compounds in which each atom has eight valence electrons, achieving a noble gas configuration.

Step 2: Evaluating Each Molecule - (Boron Trichloride):
- Boron has only 6 valence electrons in this molecule.
- It does not follow the octet rule (exception due to an incomplete octet).
- (Beryllium Hydride):
- Beryllium has only 4 valence electrons.
- It does not follow the octet rule (exception due to an incomplete octet).
- (Sulfur Hexafluoride):
- Sulfur has 12 valence electrons (expanded octet).
- It does not follow the octet rule (exception due to an expanded octet).
- (Sulfur Dichloride):
- Sulfur has 8 valence electrons (follows the octet rule).
- Each chlorine atom also completes 8 valence electrons.

Step 3: Conclusion Only follows the octet rule completely for all atoms. Thus, the correct answer is .