Explanation: The sex of a newborn baby is determined by the chromosome inherited from the father. Humans have 23 pairs of chromosomes — 22 pairs of autosomes and one pair of sex chromosomes. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The mother always contributes an X chromosome, but the father can contribute either an X or a Y. If the sperm carrying an X chromosome fertilizes the ovum, the child will be a girl (XX); if the sperm carries a Y chromosome, the child will be a boy (XY).

Explanation: Sound waves with frequencies below 20 Hz are called infrasonic waves. These waves are inaudible to the human ear but can be produced by natural phenomena such as earthquakes, volcanic eruptions, and ocean waves.

Swine Flu is caused by the H₁N₁ virus, a subtype of the Influenza A virus. It primarily affects the respiratory system and is transmitted from person to person through droplets from coughs or sneezes. Symptoms include fever, cough, sore throat, body aches, and fatigue. The H₁N₁ pandemic in 2009 was declared a global health emergency by the World Health Organization (WHO).

Other options (for context)

• Dengue: Caused by the Dengue virus, transmitted by Aedes mosquitoes.
• AIDS: Caused by the HIV (Human Immunodeficiency Virus), not H₁N₁.
• Bird flu: Caused by the H5N1 virus, not H₁N₁.

Explanation: When a man inside a moving train tosses a coin and it falls behind him, it means the train is moving forward with acceleration. The coin, after being tossed, continues to move with the train’s initial velocity, but since the train speeds up, the coin appears to fall backward relative to the man.

Explanation: The onion is a modified underground stem called a bulb. It consists of a short, disc-like stem (the basal plate) surrounded by concentric fleshy leaf bases that store food. The roots emerge from the underside of the basal plate, and new shoots grow from the center. Thus, the onion bulb serves as a storage organ for nutrients and helps in vegetative propagation.

Explanation: The Sun is seen a few minutes before actual sunrise and after actual sunset due to the refraction of light by the Earth's atmosphere. The atmosphere bends the Sun’s rays towards the Earth, making the Sun appear slightly above the horizon even when it is below it.

Explanation: Animals that live in or on trees are called arboreal animals. They are adapted to climbing and moving about among branches. Examples include monkeys, squirrels, chameleons, and tree frogs. Their adaptations may include grasping limbs, prehensile tails, claws, or adhesive pads that help them cling to tree surfaces and move efficiently among branches.

Explanation: Hardware refers to the physical components of a computer that can be seen and touched, such as the monitor, keyboard, mouse, CPU, and printer. In contrast, software consists of programs and instructions that control the hardware and perform tasks.