If a major solar storm (solar flare) reaches the Earth, which of the following are the possible effects on the Earth? 1. GPS and navigation systems could fail. 2. Tsunamis could occur at equatorial regions. 3. Power grids could be damaged. 4. Intense auroras could occur over much of the Earth. 5. Forest fires could take place over much of the planet. 6. Orbits of the satellites could be disturbed. 7. Shortwave radio communication of the aircraft flying over polar regions could be interrupted. Select the correct answer using the code given below:

1. GPS and navigation systems could fail — Correct. Solar storms disturb the ionosphere and satellite signals, degrading or disrupting GPS/navigation accuracy.

2. Tsunamis could occur at equatorial regions — Incorrect. Tsunamis are caused mainly by undersea earthquakes, volcanic eruptions or landslides, not solar flares.

3. Power grids could be damaged — Correct. Geomagnetically induced currents during major solar storms can overload transformers and damage power transmission systems.

4. Intense auroras could occur over much of the Earth — Correct. Strong geomagnetic storms can push auroral activity far beyond polar regions into much lower latitudes.

5. Forest fires could take place over much of the planet — Incorrect. Solar storms do not directly trigger widespread global forest fires as a standard Earth impact.

6. Orbits of the satellites could be disturbed — Correct. Solar activity heats and expands the upper atmosphere, increasing drag on low-Earth-orbit satellites and altering their orbits.

7. Shortwave radio communication of the aircraft flying over polar regions could be interrupted — Correct. Polar routes are especially vulnerable because solar storms can disrupt HF/shortwave radio through ionospheric disturbances.

Hence, the correct set is 1, 3, 4, 6 and 7 only.