Science M.C.Q

Both A and R are true and R is the correct explanation of A.
Explanation: Both A and R are true and R is the correct explanation of A.

Both A and R are true and R is the correct explanation of A.
Explanation: The magnetic field at the centre of circular coil is directly proportional to the current flowing through it. So if current through coil is doubled then magnetic field becomes double.

Both A and R are true but R is not the correct explanation of A.
Explanation: Vaginal pills are the chemical methods of birth control. The vaginal pills contain the chemicals called spermicides which kill the sperms.

A is false but R is true.
Explanation: A is false but R is true.

5000 KJ
Explanation: According to 10% law, the energy available to each successive trophic level is 10% of the previous trophic level.
Given, the energy available at the third trophic level = 50 KJ The energy available at second trophic level = 50 KJ x 10 = 500 K.J
Therefore, the energy available at the producer level (first trophic level) = 500 KJ x 10 = 5000 KJ

Biomass in a pond ecosystem
Explanation: The pyramid shown here is an inverted pyramid. Pyramid of energy can never be inverted. Number of producer (i.e., phytoplanktons) in a pond are always more than the consumers thus, pyramid of number in a pond cannot be inverted. In forest, biomass of producers (i.e., tree) is large, so pyramid of biomass in a forest is also upright. Pyramid of biomass for pond ecosystem is inverted as biomass of a trophic level depends on reproductive potential and longevity of its members.

220 v, 50 Hz
Explanation: The voltage in India is 220 volts, alternating at 50 cycles (Hertz) per second. The advantage of 220 is lower current and thus less power loss. And the ability to use thinner wires - less copper.

All of these 

Statement (i) is correct.
Explanation: In humans, females have homomorphic sex chromosomes, i.e., two X chromosomes. Thus, they are homogametic, i.e., produce only one type of gametes which contain X chromosomes. Sex chromosomes of human males are heteromorphic or dissimilar, i.e., XY. Fluman males are therefore heterogametic, i.e., produce two types of gametes.

Ovulation
Explanation: In general, a woman's fertile window is the day of ovulation (usually 12 to 16 days before the cycle begins) and the five days preceding it.

There are at least two different alleles for the gene for height.
Explanation: Genotype is the genetic composition of an organism, i.e., the combination of alleles it possesses. Every characte in an organism is controlled by a gene that has at least two alleles that lie on the two homologous chromosomes at the same locus. These alleles may represent the same (homozygous, e.g., TT for height)or alternate expressions (heterozygous, e.g., Tt) of the same character. Thus, if genotype for the height of an organism is Tt, this means there are at least two different alleles fo the gene for height, one is T and the other is t.

Nephron
Explanation: Nephron

A and D
Explanation: An acidic oxide will turn blue litmus red. Non-metal oxides (Oxides of S and N) are acidic in nature. Metal oxides (Oxides of Mg and Na) are basic in nature.

Tube A
Explanation: Iron nails get rusted in test tube A because both air and water are present in it. Iron nails do not get rusted in B because there is water but no air. In C, rusting will not take place because there is neither air nor water.

Potassium salts
Explanation: Potassium salts

Oxalic acid
Explanation: More than ten different types of acids, including citric acid, malic acid, ascorbic acid, and oxalic acid, are presei in tomatoes. Each 100 g serving of tomatoes contains about 50 mg of oxalic acid. So, the main acid found in tomatoes is oxali acid.