* Definition of Substance Types:
* Element (A): A pure substance consisting of only one type of atom.
* Compound (B): A substance formed when two or more elements are chemically bonded.
* Isotope (C): Atoms of the same element with different numbers of neutrons.
* Mixture (D): A combination of two or more substances that are not chemically bonded.
* Composition of Sand: Sand is composed of various small rock and mineral particles, which are physically combined but not chemically bonded.
* Conclusion: Sand is a mixture.
References:
* Properties of Mixtures: Characteristics and examples of mixtures in physical science.

1. **Understanding the Graph**: The graph provided shows the relationship between acceleration (in m/s²) and mass (in kg). The x-axis represents mass, and the y-axis represents acceleration. 2. **Observing the Trend**: The graph shows a decreasing curve, which indicates that as the mass increases, the acceleration decreases. 3. **Newton's Second Law of Motion**: According to Newton's Second Law of Motion, \( F = ma
\), where \( F \) is the force, \( m \) is the mass, and \( a \) is the acceleration. If the net force (\( F \)) is kept constant, then \( a = \frac{F}{m} \). 4. **Inverse Proportionality**: The equation \( a = \frac{F}{m} \) suggests that acceleration \( a \) is inversely proportional to the mass \( m \). This means that if the mass increases, the acceleration decreases proportionally. 5. **Conclusion**: Based on the graph and Newton's Second Law, the correct description of the relationship is that mass and acceleration are inversely proportional.
**References**: - Newton's Second Law of Motion: Basic principle in physics indicating the relationship between force, mass, and acceleration.

As comets approach the Sun, the increased solar radiation causes the ice within the comet to evaporate (a process called sublimation), releasing gas and dust particles. This creates a visible atmosphere called a coma, and the solar wind then blows this material away from the comet, forming a tail. The tail always points away from the Sun due to the force of the solar wind. References:
* NASA's Comet Exploration Missions
* "Cometary Physics" - European Space Agency Publications

The given rock layers in the illustration show a sequence from bottom to top: slate (metamorphic), siltstone (sedimentary), sandstone (sedimentary), and basalt (igneous). This sequence indicates the following geologic history:
* Metamorphic rock (slate) at the bottom suggests an initial period of high heat and pressure.
* Sedimentary rocks (siltstone and sandstone) above the slate indicate subsequent periods of deposition under water.
* Basalt (igneous) at the top suggests a volcanic eruption depositing lava that solidified into basalt.
Therefore, the correct conclusion about the geologic history of this area is that it experienced a volcanic eruption and then was located underwater.
References
* Integrated Physical Sciences: Sedimentary, metamorphic, and igneous rock formation processes.
* Geologic history interpretation based on rock layers.

1. **Wave Speeds**: The speed of different types of waves varies significantly. 2. **Gamma Waves**: These are electromagnetic waves that travel at the speed of light (approximately \( 3 \times 10^8 \) m/s). 3. **Radio Waves**: Another type of electromagnetic wave, also traveling at the speed of light. 4. **Visible Light Waves**: These are also electromagnetic waves traveling at the speed of light. 5. **Sound Waves**: Travel much slower compared to electromagnetic waves, with typical speeds in air around 343 m/s. 6.
**Conclusion**: Among the given options, sound waves travel the slowest. **References**: - Wave Speed Comparisons: Differences in propagation speeds of sound and electromagnetic waves.