A key should always be using the full spectrum of the keyspace and be extremely random. Other statements are correct. Source: WALLHOFF, John, CBK#5 Cryptography (CISSP Study Guide), April 2002 (page 6).

RC4 was designed by Ron Rivest of RSA Security in 1987. While it is officially termed “Rivest Cipher 4”, the RC acronym is alternatively understood to stand for “Ron’s Code” (see also RC2, RC5 and RC6).
RC4 was initially a trade secret, but in September 1994 a description of it was anonymously posted to the Cypherpunks mailing list. It was soon posted on the sci.crypt newsgroup, and from there to many sites on the Internet. The leaked code was confirmed to be genuine as its output was found to match that of proprietary software using licensed RC4. Because the algorithm is known, it is no longer a trade secret. The name RC4 is trademarked, so RC4 is often referred to as ARCFOUR or ARC4 (meaning alleged RC4) to avoid trademark problems. RSA Security has never officially released the algorithm; Rivest has, however, linked to the English Wikipedia article on RC4 in his own course notes. RC4 has become part of some commonly used encryption protocols and standards, including WEP and WPA for wireless cards and TLS.
The main factors in RC4’s success over such a wide range of applications are its speed and simplicity: efficient implementations in both software and hardware are very easy to develop.
The following answer were not correct choices: SHA-1 is a one-way hashing algorithms. SHA-1 is a cryptographic hash function designed by the United States National Security Agency and published by the United States NIST as a U.S. Federal Information Processing Standard. SHA stands for “secure hash algorithm”.
The three SHA algorithms are structured differently and are distinguished as SHA-0, SHA-1, and SHA-2. SHA-1 is very similar to SHA-0, but corrects an error in the original SHA hash specification that led to significant weaknesses. The SHA-0 algorithm was not adopted by many applications. SHA-2 on the other hand significantly differs from the SHA-1 hash function.
SHA-1 is the most widely used of the existing SHA hash functions, and is employed in several widely used security applications and protocols. In 2005, security flaws were identified in SHA-1, namely that a mathematical weakness might exist, indicating that a stronger hash function would be desirable. Although no successful attacks have yet been reported on the SHA-2 variants, they are algorithmically similar to SHA-1 and so efforts are underway to develop improved alternatives. A new hash standard, SHA-3, is currently under development — an ongoing NIST hash function competition is scheduled to end with the selection of a winning function in 2012.
SHA-1 produces a 160-bit message digest based on principles similar to those used by Ronald L. Rivest of MIT in the design of the MD4 and MD5 message digest algorithms, but has a more conservative design.
MD2 is a one-way hashing algorithms. The MD2 Message-Digest Algorithm is a cryptographic hash function developed by Ronald Rivest in 1989. The algorithm is optimized for 8-bit computers. MD2 is specified in RFC 1319. Although MD2 is no longer considered secure, even as of 2010 it remains in use in public key infrastructures as part of certificates generated with MD2 and RSA.
Haval is a one-way hashing algorithms. HAVAL is a cryptographic hash function. Unlike MD5, but like most modern cryptographic hash functions, HAVAL can produce hashes of different lengths. HAVAL can produce hashes in lengths of 128 bits, 160 bits, 192 bits, 224 bits, and 256 bits. HAVAL also allows users to specify the number of rounds (3, 4, or 5) to be used to generate the hash.
The following reference(s) were used for this question:
SHIREY, Robert W., RFC2828: Internet Security Glossary, may 2000. and https://en.wikipedia.org/wiki/HAVAL and https://en.wikipedia.org/wiki/MD2_%28cryptography%29 and https://en.wikipedia.org/wiki/SHA-1

A one-way hash is a function that takes a variable-length string a message, and compresses and transforms it into a fixed length value referred to as a hash value. It provides integrity, but no confidentiality, availability or authentication. Source: WALLHOFF, John, CBK#5 Cryptography (CISSP Study Guide), April 2002 (page 5).

The Diffie-Hellman algorithm is used for Key agreement (key distribution) and cannot be used to encrypt and decrypt messages. Source: WALLHOFF, John, CBK#5 Cryptography (CISSP Study Guide), April 2002 (page 4).
Note: key agreement, is different from key exchange, the functionality used by the other asymmetric algorithms.
References: AIO, third edition Cryptography (Page 632) AIO, fourth edition Cryptography (Page 709)

RC4 is a proprietary, variable-key-length stream cipher invented by Ron Rivest for RSA Data Security, Inc. Skipjack, IDEA and Blowfish are examples of block ciphers. Source: SHIREY, Robert W., RFC2828: Internet Security Glossary, may 2000.

The International Data Encryption Algorithm (IDEA) is a block cipher that operates on 64 bit blocks of data with a 128-bit key. The data blocks are divided into 16 smaller blocks and each has eight rounds of mathematical functions performed on it. It is used in the PGP encryption software. Source: WALLHOFF, John, CBK#5 Cryptography (CISSP Study Guide), April 2002 (page 3).

DES is a block encryption algorithm using 56-bit keys and 64-bit blocks that are divided in half and each character is encrypted one at a time. The characters are put through 16 rounds of transposition and substitution functions. Triple DES uses 48 rounds. Source: WALLHOFF, John, CBK#5 Cryptography (CISSP Study Guide), April 2002 (page 3).

A stream cipher treats the message as a stream of bits or bytes and performs mathematical functions on them individually. The key is a random value input into the stream cipher, which it uses to ensure the randomness of the keystream data. They are more suitable for hardware implementations, because they encrypt and decrypt one bit at a time. They are intensive because each bit must be manipulated, which works better at the silicon level. Block ciphers operate a the block level, dividing the message into blocks of bits. Cipher Block chaining (CBC) and Electronic Code Book (ECB) are operation modes of DES, a block encryption algorithm. Source: WALLHOFF, John, CBK#5 Cryptography (CISSP Study Guide), April 2002 (page 2).

Symmetric cryptography ciphers are generally fast and hard to break. So speed is one of the key advantage of Symmetric ciphers and NOT a disadvantage. Symmetric Ciphers uses simple encryption steps such as XOR, substitution, permutation, shifting columns, shifting rows, etc… Such steps does not required a large amount of processing power compare to the complex mathematical problem used within Asymmetric Ciphers.
Some of the weaknesses of Symmetric Ciphers are: The lack of automated key distribution. Usually an Asymmetric cipher would be use to protect the symmetric key if it needs to be communicated to another entity securely over a public network. In the good old day this was done manually where it was distributed using the Floppy Net sometimes called the Sneaker Net (you run to someone’s office to give them the key).
As far as the total number of keys are required to communicate securely between a large group of users, it does not scale very well. 10 users would require 45 keys for them to communicate securely with each other. If you have 1000 users then you would need almost half a million key to communicate secure. On Asymmetric ciphers there is only 2000 keys required for 1000 users. The formula to calculate the total number of keys required for a group of users who wishes to communicate securely with each others using Symmetric encryption is Total Number of Users (N) * Total Number of users minus one Divided by 2 or N (N-1)/2
Symmetric Ciphers are limited when it comes to security services, they cannot provide all of the security services provided by Asymmetric ciphers. Symmetric ciphers provides mostly confidentiality but can also provide integrity and authentication if a Message Authentication Code (MAC) is used and could also provide user authentication if Kerberos is used for example. Symmetric Ciphers cannot provide Digital Signature and Non-Repudiation.
Reference used for theis question: WALLHOFF, John, CBK#5 Cryptography (CISSP Study Guide), April 2002 (page 2).

When using symmetric cryptography, both parties will be using the same key for encryption and decryption. Symmetric cryptography is generally fast and can be hard to break, but it offers limited overall security in the fact that it can only provide confidentiality. Source: WALLHOFF, John, CBK#5 Cryptography (CISSP Study Guide), April 2002 (page 2).