Gold is a chemical element with the symbol Au (from Latin: aurum) and atomic number 79, making it one of the higher atomic number elements that occur naturally. In its purest form, it is a bright, slightly reddish yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal and a group 11 element.
We have authentic narrations in Shia and Sunni books from the Prophet Muhammad (SAWA) stating that wearing gold is not allowed for men as well as wearing pure silk. Regarding gold we have an authentic Hadeeth from Ali ibn Jafar from his brother Imam Musa ibn Jafar (AS) when he was asked: Is it allowed for man to wear gold? He replied: No, because the Prophet (SAWA) did not allow it. ( Wasaa'il al-Shia, V.4, P.415). We have also a narration from Ammar ibn Moosa from Imam Jafar Al-Sadiq (AS): man should never wear nor pray with gold. (Wasaa'il al-Shia , V4, P. 413).
In Sunni books, Tirmithi and Ibn Hanbal and many others narrated that the Prophet (SAWA) said: Silk and gold are forbidden on the men of my Ummah, permissible for their women.
That is why it is unanimous among Muslim scholars from all Muslim sects that wearing gold ands silk is forbidden for Muslim men.
Gold is not prohibited in Islam and millions of Muslim women wear gold, but Muslim men are not allowed to wear gold. Every prohibited act in Islam is damagingly harmful. Details of harm and damage are best known to Allah (SWT).
Yes. It is a matter of commitment to sell or buy.
According to our leading Maraaji' of Taqleed , it is allowed to trade online in gold, oil, and other stock exchange companies as far as the company does not do unlawful business like alcohol or usury etc. Buying and selling online is allowed.
There are two things specifically haram for men to wear in this dunya: Gold and pure silk (there are exemptions). These two items are adornments exclusively for women in this dunya, and for both men and women in the akhirah.
In addition to it being prohibited for men, if a male was to wear gold or silk in prayer, their prayer will be invalid.
There are certain studies that point to the physical harms of gold for men, like imbalance of blood cells, it being a negative mineral for males, and other such information, (for example see: http://jhsme.muq.ac.ir/article-1-15-fa.pdf) but ultimately the primary evidence are the ahadith mentioned on this issue.
And Allah knows best.