Which of the following statements are correct?
A. Two major types of resistors are wire bound resistors and carbon resistors.
B. Mobility is the drift velocity per unit electric field.
C. The internal resistance of dry cells is much lower than the common electrolytic cells.
D. In electrolytic liquids, electrons carry the electric current.
E. Potentiometer is unaffected by the internal resistance of the source.
Choose the correct answer from the options given below:

A double convex lens of refractive index 1.5 has a radius of curvature R each. The focal length of the lens is

An object approaches a convex lens from distance with a uniform speed of 3 m/s and stops at the focus. The image

An electron placed in a magnetic field of \( 3.14 \times 10^{-4} \, \text{T} \) moves in a circle. The frequency of the revolution of the electron is:

Arrange the following nuclei in the increasing order of their binding energy per nucleon: \( ^4\text{He}, ^6_3\text{Li}, ^{56}_{26}\text{Fe}, ^{238}_{92}\text{U} \)

A 10 V battery of negligible internal resistance is connected with a 200 V battery and a set of parallel resistances as shown in the figure. The value of current in the circuit.

A radioactive source is freshly prepared. It is found that it emits radiation of intensity which is 128 times the premissible safe level. The half life of this sample is 3 hours. Find the minimum time after which it would be possible to work safely with this radioactive source.

The electric potential at any point in space is given by \( V = 4x^2 \text{ volt} \). The electric field at the point (1 m, 0, 2 m) in SI unit is

When resources are unlimited in a habitat, what type of growth is seen in the population?

Read the following paragraph and answer the given questions.
Repeated amplification is achieved by the use of a thermostable DNA polymerase (isolated from a bacterium, Thermus aquaticus), which remain active during the high temperature induced denaturation of double stranded DNA. The separated DNA fragments can be visualised only after staining the DNA with a compound known as ethidium bromide followed by exposure to UV radiation. The separated bands of DNA are cut out from the agarose gel and extracted from the gel piece. The convention for naming these enzymes is the first letter of the name comes from the genus and the second two letters come from the species of the prokaryotic cell from which they were isolated, e.g., EcoRI comes from Escherichia coli RY 13. In EcoRI, the letter 'R' is derived from the name of strain. Roman numbers following the names indicate the order in which the enzymes were isolated from that strain of bacteria. Stanley Cohen and Herbert Boyer accomplished this in 1972 by isolating the antibiotic resistance gene by cutting out a piece of DNA from a plasmid which was responsible for conferring antibiotic resistance. Since the DNA is enclosed within the membranes, we have to break the cell open to release DNA, RNA, protein, polysaccharides etc. The RNA can be removed by treatment with ribonuclease whereas proteins can be removed by treatment with protease. Other molecules can be removed by appropriate treatments and purified DNA ultimately precipitates out after the addition of chilled ethanol.

In the PCR, the thermostable DNA polymerase enzyme is obtained from:

Pollen grains in majority of angiosperms are shed at:

During the p-n junction formation, when an electron diffuses from n \( \rightarrow \) p, it leaves behind an :

Read the passage carefully and answer the questions
The carbonyl group of aldehydes and ketones is highly polar. The positively charged carbon is readily attacked by electron-rich nucleophile and the negatively charged oxygen atom is attacked by an electro-deficient electrophile. Aldehydes and ketones undergo nucleophilic addition reactions in the presence of acid or a base. The mechanism involves attack of a nucleophile on the electron deficient carbonyl carbon to form a tetrahedral intermediate. A new bond is formed between the carbon and oxygen. Protonation of the anion furnished by the reaction medium yields a neutral addition product. The addition product is same whether the reaction is catalyzed by acid or a base. For example in the presence of base aldehydes and ketones react with hydrogen cyanide to form cyanohydrin.
The source of nucleophile in the base catalyzed cyanohydrin formation is: