Which of the following communication modes supports two-way traffic, but in only one direction at a time?

The correct answer is C, FTP. FTP stands for File Transfer Protocol. It opens two channels with a server, one on port 21 for commands and one on port 20 for the matter itself, and moves whole files in either direction, which is how web pages are put on a hosting server.

Option A, SMTP, carries outgoing email and can send a file only as an attachment to a letter, not as a plain transfer. Option B, Telnet, lets a user log in to a distant computer and type commands on it through port 23; it gives control of the machine but does not itself move files. Option D, IMAP, is a mail-reading protocol that keeps letters on the server. For pure file transfer the answer is always FTP, or its secure forms FTPS and SFTP.

The correct answer is B, a government body. The last part of a domain name is the top-level domain and tells you the kind of owner. Government offices use .gov, often with the country code added, as in india.gov.in for the National Portal of India.

Option A is wrong because commercial firms use .com, which stands for commercial and is the commonest domain on the web. Option C is wrong because educational institutions use .edu, and in India colleges and universities generally use ac.in for the same purpose. Option D is wrong because network providers use .net. Two more are worth remembering with these: .org for non-profit organisations and .mil for military establishments. Reading the tail of the address therefore tells a candidate at once what sort of body runs the site.

The correct answer is A, DNS. The Domain Name System is the directory of the internet. People remember names, while machines route traffic by numbers, so a DNS server looks up the name typed in the browser and returns the matching IP address before the page is fetched. It listens on port 53.

Option B, DHCP, the Dynamic Host Configuration Protocol, hands out an IP address to a machine when it joins a network; it allots addresses instead of translating names. Option C, HTTP, carries the page once the address is known and does no translation. Option D, URL, the Uniform Resource Locator, is the written address of a page and contains the domain name, but it is a form of address, not the service that resolves one. Only DNS does the conversion.

The correct answer is A, SMTP. SMTP stands for Simple Mail Transfer Protocol and is the rule set that pushes a letter out of your mail program to the server and onward from one server to the next until it reaches the receiver's mailbox. Its usual port is 25.

Option B, POP3, the Post Office Protocol version 3, works in the other direction: it downloads arriving mail to one device and normally deletes it from the server. Option C, IMAP, the Internet Message Access Protocol, also handles incoming mail, but it keeps the letters on the server so the same mailbox appears alike on every device. Option D, FTP, is the File Transfer Protocol and moves files between a computer and a server without any connection to mail. Sending is SMTP; receiving is POP3 or IMAP.

The correct answer is C, 128 bits. IPv6 was framed because the older scheme was running out of addresses, and its 128-bit length yields a pool so large that shortage is no longer a worry. Such an address is written as eight groups of hexadecimal digits separated by colons.

Option A, 32 bits, is the length of an IPv4 address, written as four decimal numbers from 0 to 255 separated by dots, and it is the distractor most often marked by mistake. Option B, 64 bits, is not the size of any IP address; it describes processor and register widths. Option D, 256 bits, is a length met in encryption keys such as AES-256, not in addressing. So remember the pair: IPv4 is 32 bits and IPv6 is 128 bits, four times as long.